The Fertilisers (Sampling and Analysis) Regulations 1996

Link to law: http://www.legislation.gov.uk/uksi/1996/1342/made/data.htm?wrap=true
Published: 1996-05-25

Statutory Instruments
1996 No. 1342

AGRICULTURE
The Fertilisers (Sampling and Analysis) Regulations 1996

Made
25th May 1996

Laid before Parliament
31st May 1996

Coming into force
21st June 1996

The Minister of Agriculture, Fisheries and Food, the Secretary of State for Scotland and the Secretary of State for Wales, acting jointly, in exercise of the powers conferred by sections 66(1), 67(5), 74A, 75(1), 76(1), 77, 78(2), (4) and (6), 79(1), (2) and (9) and 84 of the Agriculture Act 1970(1) and of all other powers enabling them in that behalf, after consultation as required by section 84(1) of the said Act with such persons or organisations as appear to them to represent the interests concerned, hereby make the following Regulations: —

Title, commencement and interpretation

1.—(1) These Regulations may be cited as The Fertilisers (Sampling and Analysis) Regulations 1996 and shall come into force on 21st June 1996.

(2) In these Regulations, unless the context otherwise requires, “the Act” means the Agriculture Act 1970 and “The Fertilisers Regulations 1991”(2) means those Regulations as amended by The Fertilisers (Amendment) Regulations 1995.(3)

(3) Any reference in these Regulations to a numbered regulation or schedule shall, unless the context otherwise requires, be construed as a reference to the regulation or schedule bearing that number in these Regulations and, in the case of a schedule, the schedule shall be read with any note thereto.

(4) Any reference in these Regulations to a numbered section shall, unless the reference is to a section of a specified Act, be construed as a reference to the section bearing that number in the Act.

Prescribed amount for the purposes of the definition of sampled portion

2.—(1) The prescribed amount of material for the purposes of the definition of sampled portion in section 66(1) shall be determined in accordance with the provisions of this regulation.

(2) In relation to solid fertiliser in a single container, the prescribed amount shall be the contents of the container.

(3) In relation to solid fertiliser in more than one container —

(a)if all the containers together hold less than 5 tonnes, the prescribed amount shall be the contents of all the containers;

(b)if any container holds at least 5 tonnes, the prescribed amount shall be 5 tonnes; and

(c)if neither sub-paragraph (a) nor (b) above applies, the prescribed amount shall be the contents of the lowest number of containers together holding at least 5 tonnes.

(4) In relation to solid fertiliser which is loose in a single heap or bay, the prescribed amount shall be the contents of the heap or bay.

(5) In relation to solid fertiliser which is loose in more than one heap or bay —

(a)if all the heaps and bays together hold less than 5 tonnes, the prescribed amount shall be the contents of all the heaps and bays;

(b)if each heap and bay holds at least 5 tonnes, the prescribed amount shall be the contents of any one of the heaps or bays; and

(c)in a case where neither sub-paragraph (a) nor (b) above applies, the prescribed amount shall be the contents of a number of the heaps or bays together holding at least 5 tonnes.

(6) In relation to fluid fertiliser in a single container, the prescribed amount shall be the contents of the container.

(7) In relation to fluid fertiliser in more than one container —

(a)if all the containers together hold less than 5,000 litres, the prescribed amount shall be the contents of all the containers;

(b)if any container holds at least 5,000 litres, the prescribed amount shall be 5,000 litres; and

(c)if neither subparagraph (a) nor (b) above applies, the prescribed amount shall be the contents of the lowest number of containers together holding at least 5,000 litres.

Manner of taking, marking, sealing and fastening up of samples

3.  The manner in which samples are to be taken, marked, sealed and fastened up in cases where under Part IV of the Act they are taken in the prescribed manner shall be as set out in Schedule 1.

Methods of sending part of a sample

4.  Any part of a sample required to be sent to any person in pursuance of subsection (1)(b) or (2) of section 77 shall be sent by registered post or by the recorded delivery service or be delivered or given by hand.

Qualifications of agricultural analysts and deputy agricultural analysts

5.  The prescribed qualifications for an agricultural analyst or a deputy agricultural analyst for the purposes of section 67(5) and for the purposes of these Regulations are that he shall possess a Mastership in Chemical Analysis awarded by the Royal Society of Chemistry or be a Chartered Chemist, being a Fellow or a Member of the Royal Society of Chemistry, and that his practical experience of the analysis and examination of fertilisers shall be attested by another agricultural analyst or deputy agricultural analyst appointed under section 67(3) of the Act or in accordance with section 11 of the Fertilisers and Feeding Stuffs Act 1926.(4)

Application of the methods of analysis

6.—(1) The methods by which analysis of fertilisers shall be made for the purposes of the Act shall be those set out in Schedule 2 in accordance with the following provisions of this regulation.

(2) Analytical constituents of materials listed in Groups 1(a), 2(a) and 3(a) of Section A, Groups 1 to 4 of Section B, Groups 1(a), 1(b) and 2 of Section C, Section D and Section E, of the table in Schedule 1 to the Fertilisers Regulations 1991 shall be determined by the appropriate methods of analysis prescribed in Part 1 of Schedule 2.

(3) Subject to paragraph (4) below, analytical constituents of any materials other than those referred to in paragraph (2) of this regulation shall be determined by the appropriate methods of analysis prescribed in Part 2 of Schedule 2, save that the following analytical constituents shall be determined by the appropriate methods prescribed in Part 1 of Schedule 2:

(a)the amount of total phosphorus soluble in mineral acids;

(b)the amount of phosphorus soluble in 2% formic acid;

(c)the amount of phosphorus soluble in 2% citric acid;

(d)the amount of phosphorus in any fertiliser extract; and

(e)the amount of any trace element in any fertiliser extract.

(4) In the case of “Basic slag medium concentration” and “Granular basic slag” in Group 2(b) of Section A of the said table, fineness shall be determined by the appropriate method prescribed in Part 1 of Schedule 2.

Form of certificate of analysis

7.  The certificate of an agricultural analyst of the analysis shall be in the form set out in Schedule 3.

Modification of the Agriculture Act 1970

8.  In relation to any material to which these Regulations apply the operation of the provisions of sections 66(1) and 76(5) shall be modified as follows: —

(a)in the definition of “sampled portion” in section 66(1) for the words “five tons or 1,000 gallons or the prescribed metric substitution” there shall be substituted the words “five tonnes or 5,000 litres”.

(b)in section 76(5), for the words “fourteen pounds or the prescribed metric substitution” there shall be substituted the words “six kilograms”.

Revocations

9.  The Fertilisers (Sampling and Analysis) Regulations 1991(5), the Fertilisers (Sampling and Analysis) (Amendment) Regulations 1991(6) and the Fertilisers (Sampling and Analysis) (Amendment) Regulations 1994(7) are hereby revoked.

Angela Browning
Parliamentary Secretary, Minister of Agriculture, Fisheries and Food
22nd May 1996

Lindsay
Parliamentary Under Secretary of State,
Scottish Office
25th May 1996

Gwilym Jones
Parliamentary Under Secretary of State,
Welsh Office
24th May 1996

Regulation 3

SCHEDULE 1MANNER OF TAKING, MARKING, SEALING AND FASTENING UP OF SAMPLES

PART IDEFINITIONS

In this Schedule: —
“sampled portion” means a quantity of a material constituting a unit and having characteristics presumed to be uniform;

“incremental sample” means a quantity taken from one point in the sampled portion;

“aggregate sample” means an aggregate of incremental samples taken from the same sampled portion;

“reduced sample” means a representative part of the aggregate sample obtained from the latter by a process of reduction; and

“final sample” means a representative part of the reduced sample or, where no intermediate reduction is required, of the aggregate sample.


PART IIGENERAL INSTRUCTIONS FOR THE TAKING OF SAMPLES

1.  In the case of fertiliser in containers, only unopened containers which appear to the inspector proposing to take the sample to be the original containers of the fertiliser shall be selected for the purpose of sampling.

2.  The sample shall be taken and prepared as quickly as possible having regard to the precautions necessary to ensure that it remains representative of the sampled portion. Instruments, surfaces and containers used in sampling shall be clean and dry.

3.  No sample shall be drawn from any part of the sampled portion which appears to be damaged.

4.  When stones are naturally present in a fertiliser, they shall, if possible, be broken up and mixed with the quantity from which a sample is to be drawn. Failing this they shall be removed from the mixture from which a sample is to be drawn and the weight of the residue of that mixture and the weight of the stones ascertained and reported to the analyst. In addition, a representative sample of the stones shall be sent to the analyst with the final sample.

5.  An inspector who intends to take a sample in accordance with the provisions of section 76(1) on premises (not being premises used only as a dwelling) on which he has reasonable cause to believe that there is any fertiliser which the occupier of the premises has purchased, shall: —

(a)satisfy himself that the conditions in which the fertiliser is stored are not such as might cause undue deterioration of the said fertiliser and that the fertiliser appears not to have been contaminated by any other material;

(b)where he has reasonable cause to believe that fertiliser in containers is only part of an original consignment, select the number of containers to be sampled as if not less than the whole consignment were still present, except that sampling shall not take place if fewer than the minimum number of containers prescribed in Table 1 of Part VI for the purposes of paragraph 2(a) and (c) of Part III of this Schedule are present.

The provisions of this paragraph shall not apply as respects any fertiliser purchased for the purpose of resale in the course of trade.

6.  The sampling apparatus shall be made of materials which cannot affect the characteristics of the materials to be sampled.

7.  In the case of a sampling spear its dimensions shall be appropriate to the characteristics of the sampled portion in all respects including dimensions of the container and particle size of the fertiliser.

8.  Notwithstanding the provisions of these Regulations, a sampling spear shall not be used if, prior to the taking of a sample, objection is raised thereto by the manufacturer on the grounds that the material is unsuitable.

9.  Mechanical apparatus may be used for the sampling of moving fertilisers, if the apparatus is capable of taking samples right across the flow of the product.

10.  Apparatus designed to divide the sample into approximately equal parts may be used for taking incremental samples and for the preparation of reduced and final samples.

11.  A sample taken in accordance with the methods described below shall be deemed to be representative of the sampled portion.

PART IIIQUANTITATIVE REQUIREMENTS

Sampled portion

1.  The sampled portion in compliance with regulation 2 shall be such that each of its constituent parts can be sampled in accordance with the requirements of this Schedule.

Incremental sample

2.  The incremental samples shall be selected in the following manner: —

(a)in the case of solid fertilisers in containers —

(i)where the content of each of the containers in the sampled portion is greater than 1kg in weight, the number of containers shall be selected in accordance with Table 1 in Part VI of this Schedule;

(ii)where the content of each of the containers in the sampled portion does not exceed 1kg in weight, the number of containers shall be selected in accordance with Table 1 in Part VI of this Schedule, except that the number selected shall be not less than four;

(b)in the case of loose solid fertilisers the number of incremental samples shall be selected in accordance with Table 2 in Part VI of this Schedule;

(c)in the case of fluid fertilisers —

(i)where each container in the sampled portion contains not more than 100 litres the number of containers shall be selected in accordance with Table 3 in Part VI of this Schedule;

(ii)where each container in the sampled portion contains more than 100 litres an incremental sample shall be drawn from each container.

Aggregate sample

3.  The weight or volume, as appropriate, of the aggregate sample shall be not less than the following: —

(a)solid fertilisers in containers —

(i)containers of more than 1 kg

4 kg

(ii)containers not exceeding 1 kg (subject to sub-paragraph (iii) below)

2 kg

(iii)containers of ammonium nitrate sampled for testing in accordance with method 14 in Part I of Schedule 2

4 kg

(b)loose solid fertilisers

4 kg

(c)fluid fertilisers —

(i)containers exceeding 250,000 litres

5 litres

(ii)containers exceeding 1 litre but not exceeding 250,000 litres

4 litres

(iii)containers not exceeding 1 litre

2 litres

Final sample

4.  The weight or volume, as appropriate, of each final sample shall not be less than the following: —

(a)solid fertilisers (except as mentioned in sub-paragraph (b) below)

500 g

(b)ammonium nitrate fertilisers sampled for testing in accordance with method 14 in Part I of Schedule 2

1 kg

(c)fluid fertilisers

500 ml

PART IVTAKING AND PREPARATION OF SAMPLES

Incremental samples

1.  Incremental samples of approximately equal sizes shall be taken at random throughout the whole sampled portion in the following manner: —

(a)in the case of solid fertilisers in containers —

(i)having selected the required number of containers for sampling in accordance with paragraph 2(a) of Part III of this Schedule, part of the content of each selected container shall be taken as the incremental sample, except in the case of material to which sub-paragraph (iv) of this paragraph applies;

(ii)where necessary, each selected container shall be emptied and worked up with a shovel separately and one shovelful taken as the incremental sample;

(iii)when the material is of a suitable nature the incremental sample may be taken from each selected container by means of a sampling spear or by divider;

(iv)when the material is so packed or of such a nature that a shovel or spear or divider cannot be used, or where the content of the container does not exceed 1kg, the whole container shall be taken as the incremental sample;

(v)where the fertiliser is in a coarse or lumpy condition incremental samples shall be taken in accordance with sub-paragraph (ii) or (iv) of this paragraph as appropriate. These shall be crushed immediately and the whole passed through a sieve with meshes 31.8mm square;

(vi)where the fertiliser consists of bulky material, uneven in character and likely to get matted together, each selected package shall be emptied separately and the matted portions torn up and the whole of the contents of each package shall be thoroughly mixed. The incremental samples shall then be taken in accordance with sub-paragraphs (ii) or (iv) of this paragraph as appropriate;

(b)in the case of loose solid fertilisers —

(i)an imaginary division shall be made of the sampled portion into a number of approximately equal parts, corresponding to the number of incremental samples required in accordance with Table 2 in Part VI of this Schedule and at least one incremental sample shall be taken at random from each of these parts;

(ii)when sampling is being carried out while the material comprising the sampled portion is in motion, the incremental samples shall be taken from the approximately equal parts as required in sub-paragraph (b)(i) of this paragraph;

(iii)when a sampling spear is used the sample shall be taken at an angle to the base of the heap;

(iv)where the fertiliser is in a coarse or lumpy condition, or consists of bulky material, uneven in character and likely to get matted together, the incremental samples shall be taken in accordance with the relevant provisions of paragraph 1(a)(v) or 1(a)(vi), as appropriate;

(v)where it is not possible to comply with the requirements of paragraph 1 of Part III of this Schedule when sampling fertilisers in bulk, the sampling should be carried out when the sampled portion is loaded or unloaded. In this case samples shall be taken from the randomly selected notional parts, as defined in sub-paragraph (b)(i) of this paragraph, while these are being moved;

(c)in the case of fluid fertilisers in containers each containing not more than 100 litres, the number of containers to be selected shall be taken in accordance with Table 3 in Part VI of this Schedule and —

(i)where the containers each contain not more than 1 litre the entire contents of the selected containers shall be transferred into a clean dry vessel of suitable material;

(ii)where the containers each contain more than 1 litre and not more than 100 litres the selected containers shall be well shaken or the contents agitated or otherwise treated to ensure uniformity. An approximately equal proportion of fluid shall then be taken immediately from each of the selected containers and transferred into a clean dry vessel of suitable material;

(d)in the case of fluid fertilisers in containers each containing more than 100 litres —

(i)when a consignment is being withdrawn from the container and there is a tap in the outlet pipe from which it is suitable to draw a sample, a quantity of not less than 4 litres shall be drawn from the tap (after first withdrawing sufficient to remove any residues in the pipe) into a clean dry vessel of suitable material, made up of portions not less than 0.5 litres and of approximately equal size taken at regular intervals; otherwise

(ii)if the liquid is homogeneous, about 1 litre shall be drawn from a convenient outlet in the container (after first withdrawing sufficient to remove any residues in the outlet) into a clean dry vessel of suitable material, or

(iii)if the liquid is not homogeneous, the contents shall be well stirred or otherwise agitated and sampling shall then proceed as in sub-paragraph (ii), but

(iv)if it is not possible to make the liquid homogeneous, in the manner described in sub-paragraph (iii), or if the inspector considers that the procedure in sub-paragraphs (i), (ii) and (iii) may not be appropriate, the contents shall be sampled by lowering an open tube (which must be long enough to reach the bottom of the container) perpendicularly into the container. One or both ends of the tube shall then be closed and the contents transferred into a clean dry vessel of suitable material. If sampling by tube is impracticable, portions shall be taken from various levels of the container with a sampling bottle so as to obtain a quantity fairly representative of the whole. The appropriate process shall be repeated until a quantity of not less than 4 litres has been withdrawn;

(v)where a sampled portion consists of two or more containers, incremental samples of approximately equal size shall be taken from each, drawn in the manner described in sub-paragraphs (i), (ii), (iii) or (iv), as appropriate, and shall be placed in a clean dry vessel of suitable material.

Aggregate sample

2.  The incremental samples shall be thoroughly mixed to form a single aggregate sample. In the case of solid fertilisers the material in the aggregate sample shall be carefully mixed to obtain an homogenised sample. Any lumps inconsistent with the nature of the material shall be broken up (if need be by separating them out and returning them to the aggregate sample).

Reduced sample

3.—(a) In the case of solid fertilisers the aggregate sample shall, if necessary, be reduced to not less than 2 kg, or 4 kg for ammonium nitrate fertilisers sampled for testing in accordance with method 14 in Part I of Schedule 2, in the following manner: —

(i)the material shall be heaped to form a “cone”, which shall then be flattened and quartered. Two diagonally opposite quarters shall be rejected and the remainder shall then be mixed and the quartering and rejection continued as necessary; or

(ii)the reduction method effected by the use of a mechanical device.

(b)In the case of fluid fertilisers if the aggregate sample consists of approximately 2 litres this may be taken as the reduced sample. In all other cases the aggregate sample shall be thoroughly mixed and a quantity of at least 2 litres transferred immediately into a clean dry vessel of suitable material.

Final samples

4.  The final samples shall be obtained in the following manner: —

(a)in the case of solid fertilisers, the reduced sample or where necessary the aggregate sample shall be thoroughly mixed and divided into three or, in the circumstances set out in section 77(2), four similar and approximately equal parts, and each part placed in an appropriate airtight container;

(b)in the case of fluid fertilisers the reduced sample or where necessary the aggregate sample shall be thoroughly mixed and at once divided into three or, in the circumstances set out in section 77(2), divided into four similar and approximately equal parts by pouring successive portions into appropriate airtight containers.

The containers used shall be such that the characteristics of the fertiliser at the time of sampling are preserved. In the case of a sample e.g. ammonium nitrate which is to be tested for particle size, precautions shall be taken to ensure that the physical condition of the sample does not change between sampling and testing. Where any void would occur within the sample container the sample may be placed in a plastic bag before being put in the final container and in that event the void shall be filled with a neutral product which will not affect either the physical or chemical composition of the sample. For the tests specified in Part I of Schedule 2, Methods 14 a-g, the final samples shall be kept at a temperature between 0 C and 25 C.

PART VMARKING, SEALING AND FASTENING UP OF THE FINAL SAMPLE

1.  Each container of a final sample shall be so secured and sealed by the person taking the sample that the container cannot be opened without breaking the seal; alternatively the container may be placed in a stout envelope or in a linen, cotton or plastic bag, and this further receptacle then secured and sealed in such a manner that the contents cannot be removed without breaking the seal or the receptacle.

2.  A label shall be attached to the container or receptacle containing the final sample and sealed in such a manner that it cannot be removed without the seal being broken. The label shall be marked with the following particulars, which shall be visible without the seal being broken: —

(a)name of the inspector as well as the department to which he belongs;

(b)identification mark given by the inspector to the sample;

(c)place of sampling;

(d)date of sampling;

(e)name of the material; and

(f)identification code, batch reference number or consignment identification of the material sampled, where readily available.

3.  The container or receptacle may also be sealed, or the label also signed or initialled, by the holder of the material sampled or person acting on his behalf.

PART VISAMPLING TABLES

TABLE 1

FERTILISERS IN CONTAINERS

Number of containers in the sampled portion
Number of containers to be selected for sampling

1 to 4
All containers

5 to 16
not less than 4

17 to 25
not less than 5

26 to 36
not less than 6

37 to 49
not less than 7

50 to 64
not less than 8

65 to 81
not less than 9

82 to 100
not less than 10

101 to 121
not less than 11

122 to 144
not less than 12

145 to 169
not less than 13

170 to 196
not less than 14

197 to 225
not less than 15

226 to 256
not less than 16

257 to 289
not less than 17

290 to 324
not less than 18

325 to 361
not less than 19

362 and above
not less than 20

TABLE 2

LOOSE FERTILISERS

Size of sampled portion in tonnes
Number of incremental samples required

Up to and including 2.5
not less than 7

Greater than 2.5 and up to and including 3
not less than 8

Greater than 3 and up to and including 4
not less than 9

Greater than 4 and up to and including 5
not less than 10

Greater than 5 and up to and including 6
not less than 11

Greater than 6 and up to and including 7
not less than 12

Greater than 7 and up to and including 8
not less than 13

Greater than 8 and up to and including 9
not less than 14

Greater than 9 and up to and including 11
not less than 15

Greater than 11 and up to and including 12
not less than 16

Greater than 12 and up to and including 14
not less than 17

Greater than 14 and up to and including 16
not less than 18

Greater than 16 and up to and including 18
not less than 19

Greater than 18 and up to and including 20
not less than 20

Greater than 20 and up to and including 22
not less than 21

Greater than 22 and up to and including 24
not less than 22

Greater than 24 and up to and including 26
not less than 23

Greater than 26 and up to and including 28
not less than 24

Greater than 28 and up to and including 31
not less than 25

Greater than 31 and up to and including 33
not less than 26

Greater than 33 and up to and including 36
not less than 27

Greater than 36 and up to and including 39
not less than 28

Greater than 39 and up to and including 42
not less than 29

Greater than 42 and up to and including 45
not less than 30

Greater than 45 and up to and including 48
not less than 31

Greater than 48 and up to and including 51
not less than 32

Greater than 51 and up to and including 54
not less than 33

Greater than 54 and up to and including 57
not less than 34

Greater than 57 and up to and including 61
not less than 35

Greater than 61 and up to and including 64
not less than 36

Greater than 64 and up to and including 68
not less than 37

Greater than 68 and up to and including 72
not less than 38

Greater than 72 and up to and including 76
not less than 39

Greater than 76
not less than 40

TABLE 3

FLUID FERTILISERS

Number of containers in sampled portion
Number of containers to be selected for sampling

1 to 3
All containers

4 to 20
not less than 4

21 to 60
not less than 6

61 to 100
not less than 8

101 to 400
not less than 10

More than 400
not less than 20

Regulation 6

SCHEDULE 2METHODS OF ANALYSIS

PART I

General

1.  When two or more methods are prescribed in this part of this Schedule to determine a component of a fertiliser the choice of the method shall, except where otherwise indicated, be left to the agricultural analyst concerned; the method used must however be indicated in the certificate of analysis.

Reagents

2.  Except where otherwise specified in the method of analysis, all reagents shall be of analytical quality. Where trace elements are to be determined, the purity of the reagents used shall be checked by means of a blank test.

Water

3.—(a) Except where otherwise specified, a reference in this Part of this Schedule to water shall be a reference to demineralized or distilled water.

(b)For the determination of any form of nitrogen, water shall be free of all nitrogenous compounds and carbon dioxide.

(c)Except where the method of analysis specifies a particular solvent or diluent, all dissolution, dilution, rinsing and washing operations mentioned in the methods of analysis shall be carried out using water.

Apparatus

4.—(a) Only special instruments and apparatus and specifically required apparatus and equipment are mentioned in the methods of analysis.

(b)Apparatus and equipment shall be clean.

(c)The accuracy of graduated glassware shall be assured by reference to the appropriate standards.

Methods of Analysis

1.
Preparation of the sample for analysis

2.
Determination of ammoniacal nitrogen

3.a
Determination of nitrate and ammoniacal nitrogen — Ulsch method

b
Determination of nitrate and ammoniacal nitrogen — Arnd method

c
Determination of nitrate and ammoniacal nitrogen — Devarda method

4.a
Determination of total nitrogen in calcium cyanamide — in the absence of nitrate

b
Determination of total nitrogen in calcium cyanamide — in the presence of nitrate

5.
Determination of total nitrogen in urea

6.
Determination of cyanamide nitrogen

7.
Determination of biuret in urea

8.a
Determination of different forms of nitrogen in the same sample — in the presence of cyanamide nitrogen

b
Determination of different forms of nitrogen in the same sample — in the absence of cyanamide nitrogen

9.a
Extraction of total phosphorus — by mineral acids

b
Extraction of phosphorus — by 2% formic acid

c
Extraction of phosphorus — by 2% citric acid

d
Extraction of phosphorus — by neutral ammonium citrate

e
Extraction of phosphorus — by alkaline ammonium citrate (Petermann’s method) at 65 C

f
Extraction of phosphorus — by alkaline ammonium citrate (Petermann’s method) at ambient temperature

g
Extraction of phosphorus — by alkaline ammonium citrate (Joulie’s method)

h
Extraction of phosphorus — by water

10.
Determination of extracted phosphorus

11.
Determination of water-soluble potassium

12.
Determination of chlorides in the absence of organic material

13.a
Determination of fineness of grinding — dry method

b
Determination of fineness of grinding of soft natural phosphates

14.
Methods of analysis and test procedures for ammonium nitrate fertilisers containing more than 28% nitrogen by weight

a
Method for the application of thermal cycles

b
Determination of the oil retention value

c
Determination of combustible ingredients

d
Determination of the pH value

e
Determination of the particle size

f
Determination of the chlorine content (as chloride ion)

g
Determination of copper

15.
Extraction of total calcium, total magnesium, total sodium and total sulfur in the form of sulfates

16.
Extraction of total sulfur

17.
Extraction of water-soluble calcium, magnesium, sodium and sulfur (in the form of sulfates)

18.
Extraction of water-soluble sulfur

19.
Extraction and determination of elemental sulfur

20.
Manganimetric determination of extracted calcium following precipitation in the form of oxalate

21.
Determination of magnesium by atomic absorption spectrometry

22.
Determination of magnesium by complexometry

23.
Determination of sulfates

24.
Determination of the sodium extracted

25.
Trace elements at a concentration less than 10%

a
Extraction of total trace elements

b
Extraction of water-soluble trace elements

c
Removal of organic compounds from fertiliser extracts

d
Determination of trace elements in fertiliser extracts by atomic absorption spectrometry (general procedure)

e
Determination of boron in fertiliser extracts by means of spectrometry with azomethine-h

f
Determination of cobalt in fertiliser extracts by atomic absorption spectrometry

g
Determination of copper in fertiliser extracts by atomic absorption spectrometry

h
Determination of iron in fertiliser extracts by atomic absorption spectrometry

i
Determination of manganese in fertiliser extracts by atomic absorption spectrometry

j
Determination of molybdenum in fertiliser extracts by spectrometry of a complex with ammonium thiocyanate

k
Determination of zinc in fertiliser extracts by atomic absorption spectrometry

26.
Trace elements at a concentration greater than 10%

a
Extraction of total trace elements

b
Extraction of water — soluble trace elements

c
Removal of organic compounds from fertiliser extracts

d
Determination of trace elements in fertiliser extracts by atomic absorption spectrometry (general procedure)

e
Determination of boron in fertiliser extracts by means of acidimetric titration

f
Determination of cobalt in fertiliser extracts by the gravimetric method with 1-nitroso-2-naphthol

g
Determination of copper in fertiliser extracts by the titrimetric method

h
Determination of iron in fertiliser extracts by atomic absorption spectrometry

i
Determination of manganese in fertiliser extracts by titration

j
Determination of molybdenum in fertiliser extracts by the gravimetric method with 8-hydroxyquinoline

k
Determination of zinc in fertiliser extracts by atomic absorption spectrometry

1.PREPARATION OF THE SAMPLE FOR ANALYSIS

SCOPE

1.  The following procedure is to be used for the preparation of the sample for analysis, taken from the final sample.

2.    PRINCIPLE

Solid fertilisers: the preparation of a final sample received at the laboratory is a series of operations, usually sieving, grinding and mixing, carried out in such a way that: —

(a)the smallest amount weighed out laid down by the methods of analysis is representative of the laboratory sample; and

(b)the fineness of the fertiliser has not been changed by the preparation to the extent that its solubility in the various extraction reagents is appreciably affected.

Fluid fertilisers: the final sample is mixed by shaking to ensure that any insoluble matter, particularly crystalline material, is thoroughly dispersed before each test portion is taken.

3.    APPARATUS

Sample divider (optional).

Sieves with apertures of 0.2 mm and 0.5 mm.

250 ml flasks, stoppered.

Porcelain pestle and mortar or grinder.

CHOICE OF TREATMENT TO BE USED

4.  Preliminary remark: if the product is suitable, only a representative part of the final sample need be kept.

Final samples which must not be ground

4.  Calcium nitrate, calcium magnesium nitrate, sodium nitrate, Chile nitrate, calcium cyanamide, nitrogenous calcium cyanamide, ammonium sulfate, ammonium nitrates of over 30% N, urea, basic slag, natural phosphate rendered partially soluble, precipitated dihydrated dicalcium phosphate, calcined phosphate, aluminium calcium phosphate, soft ground rock phosphate.

Finals samples which must be divided and part of which must be ground

4.2  These are products in respect of which certain determinations are carried out without previous grinding (fineness of grinding for example) and other determinations after grinding. They include all compound fertilisers containing the following phosphate ingredients: basic slag, aluminium calcium phosphate, calcined phosphate, soft ground rock phosphate and natural phosphate rendered partially soluble. To that end, divide the final sample into two parts, which are as identical as possible, using a sample divider or by quartering.

Final samples in respect of which all determinations are carried out on a grounded product

4.3  These are all the other fertilisers on the list which are not to be found under 4.1 and 4.2. The whole final sample shall be ground.

METHOD

5.  The part of the final sample referred to under 4.2 and 4.3 is sieved rapidly through a sieve with apertures of 0.5 mm. The residue is ground roughly as to obtain a product in which there is a minimum of fine particles, and it is then sieved. The grinding must be done in conditions such that the substance is not appreciably heated. The operation is repeated as many times as is necessary until there is no residue, and it must be effected as quickly as possible in order to prevent any gain or loss of constituents (water, ammonia). The whole ground and sieved product is placed in a non-corrodable container provided with an air-tight closure.

Before any weighing is carried out for the analysis, the whole sample must be thoroughly mixed.

SPECIAL CASES

6.—(a) Fertilisers comprising a blend of several categories of crystals

In this case, separation frequently occurs. It is therefore absolutely essential to crush and pass the sample through a sieve with apertures of 0.2 mm (for example, mixtures of ammonium phosphate and potassium nitrate). The grinding of the whole of the final sample is recommended in the case of these products.

(b)Residue which is difficult to grind and does not contain fertilising substances

Weigh the residue and take account of its mass when calculating the final result.

(c)Products which decompose on heating

Grinding must be carried out in such a way as to avoid any heating. It is preferable in this case to use a mortar for grinding (for example, compound fertilisers containing calcium cyanamide and urea).

(d)Products which are abnormally moist or made into a paste by grinding

To ensure homogeneity, a sieve is to be chosen which has the smallest apertures compatible with the destruction of lumps by hand or with the pestle. This may be the case for mixtures, certain ingredients of which contain water of crystallisation.

FLUID FERTILISERS

7.  Mix thoroughly by shaking, ensuring that any insoluble matter, particularly crystalline material, is thoroughly dispersed, immediately before drawing a portion of the sample of analysis.

2.DETERMINATION OF AMMONIACAL NITROGEN

SCOPE

1.  This method is for the determination of ammoniacal nitrogen.

FIELD OF APPLICATION

2.  All nitrogenous fertilisers, including compound fertilisers, in which nitrogen is found exclusively either in the form of ammonium salts, or ammonium salts together with nitrates.

It is not applicable to fertilisers containing urea, cyanamide or other organic nitrogenous compounds.

PRINCIPLE

3.  Displacement of ammonia by means of an excess of sodium hydroxide; distillation; determination of the ammonia absorbed by a given volume of a standard sulfuric acid and titration of the excess acid with a standard solution of sodium or potassium hydroxide.

4.    REAGENTS

Hydrochloric acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid (p=1.18 g/ml) with an equal volume of water.

Sulfuric acid, 0.05 M solution

for variant (a) (see page 16)

Sodium or potassium hydroxide, 0.1 M solution, carbonate free

Sulfuric acid, 0.1 M solution

for variant (b) (see page 16)

Sodium or potassium hydroxide, 0.2 M solution, carbonate free

Sulfuric acid, 0.25 M solution

for variant (c) (see page 16)

Sodium or potassium hydroxide, 0.5 M solution, carbonate free

Sodium hydroxide solution, 30 g per 100 ml, ammonia free

Indicator solutions:

Mixed indicator:

4.9.1 Solution A: dissolve 1 g methyl red in 37 ml sodium hydroxide solution 0.1 M and make up to 1 litre with water.

Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of solution A and 2 volumes of solution B.

This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops) of this indicator solution.

Methyl red indicator solution:

4.9.2 Dissolve 0.1 g methyl red in 50 ml ethanol (95%) make up to 100 ml with water and filter if necessary. This indicator may be used (4 to 5 drops) instead of the preceding one.

4.10 Anti-bump granules of pumice stone, washed in hydrochloric acid and ignited.

4.11 Ammonium sulfate.

5.    APPARATUS

Distillation apparatus consisting of a round-bottomed flask of suitable capacity connected to a condenser by means of a splash head.

Examples of the different types of equipment recommended for this determination are reproduced in Figures 1, 2, 3 and 4 in the Appendix.

Rotary shaker, 35 to 40 turns per minute.

PREPARATION OF SAMPLE

6.  See Method 1.

PROCEDURE

Solubility test

7.—7.1.1 Carry out a solubility test on the sample in water at room temperature in the proportion of 2 g per 100 ml.

Preparation of the solution

7.1.2 Weigh 5, 7 or 10 g of the sample to the nearest 0.001 g, as shown in the Table, and place in a 500 ml graduated flask. From the result of the solubility test, proceed as follows:

(a) Products completely soluble in water

(a)Add sufficient water to dissolve the sample; shake, and when completely dissolved, make up to volume and mix thoroughly.

(b) Products not completely soluble in water

(b)Add 50 ml water and then 20 ml hydrochloric acid solution (4.1). Swirl and leave undisturbed until the evolution of carbon dioxide has ceased. Add 400 ml water and shake for half an hour on the rotary shaker (5.2). Make up to volume with water, mix and filter through a dry paper into a dry receiver. Discard the first portion of the filtrate.

Determination

7.2  According to the variant chosen, place in the collecting flask a measured quantity of standard sulfuric acid as indicated in the Table on page16. Add the appropriate quantity of the chosen indicator solution (4.9.1 to 4.9.2) and, if necessary, water to obtain a volume of at least 50 ml. The condenser outlet must be below the surface of the standard acid in the collecting flask.

Transfer by pipette, according to the details given in the Table, an aliquot portion of the clear solution into the distillation flask of the apparatus. Add water to obtain a volume of about 350 ml and several grains of pumice to control the boiling.

Assemble the distillation apparatus and, taking care to avoid any loss of ammonia, add to the contents of the distillation flask 10 ml of concentrated sodium hydroxide solution (4.8) or 20 ml of the reagent in the cases where 20 ml hydrochloric acid (4.1) have been used in order to dissolve the sample. Warm the flask gently and when boiling commences distil at such a rate that about 200 ml are obtained in 30 minutes.

When no more ammonia is likely to be evolved, lower the receiving flask so that the tip of the condenser is above the surface of the liquid.

Test the subsequent distillate by means of an appropriate reagent to ensure that all the ammonia has been completely distilled. Wash the condenser with a little water and titrate the excess acid with the standard solution of sodium or potassium hydroxide prescribed for the variant adopted (see Note).

Note:Standard solutions of different strengths may be used for the titration provided that the volumes used do not, as far as possible, exceed 40 to 45 ml.

Blank

7.3  Carry out a blank test under the same conditions (omitting only the sample) and allow for this in the calculation of the final result.

Control test

7.4  Before carrying out analyses, check that the apparatus is working properly and that the correct application of the method is used by taking an aliquot portion of a freshly prepared solution of ammonium sulfate (4.11) containing the maximum quantity of nitrogen prescribed for the chosen variant.

EXPRESSION OF RESULT

8.  Express the result of the analysis as the percentage of ammoniacal nitrogen in the fertiliser as received for analysis using the formula

%N =
(50 – A) × F for variants (a) and (b) and

%N =
(35 – A) × F for variant (c)

where
50 (or 35 where variant (c) applies)

=
millilitres of standard solution of sulfuric acid in the receiving flask.

A =
millilitres of sodium or potassium hydroxide used for the titration.

F =
factor taking into account the weight of sample, the dilution, the volume of the aliquot portion distilled and the volumetric equivalent.

TABLE FOR METHOD 2

Determination of the ammoniacal nitrogen and of the ammoniacal and nitrate nitrogen in fertilisers. Table of the weighing, dilution and calculation to be carried out for each of the variants (a), (b) and (c) of the method.

Variant (a), —
Approximate maximum quantity of nitrogen to be distilled = 50 mg

Sulfuric acid 0.05 M to be placed in the receiving flask = 50 ml

Titration with sodium or potassium hydroxide, 0.1 M solution

Declaration N%
Amount to be weighed (g)
(Volume) Dilution (ml)
Volume of sample solution to be distilled (ml)
Factor F

0 – 5
10
500
50
0.14

5 – 10
10
500
25
0.28

10 – 15
7
500
25
0.40

15 – 20
5
500
25
0.56

20 – 40
7
500
10
1.00

Variant (b), —
Approximate maximum quantity of nitrogen to be distilled = 100 mg

Sulfuric acid 0.1 M to be placed in the receiving flask = 50 ml

Titration with sodium or potassium hydroxide, 0.2 M solution

Declaration N%
Amount to be weighed (g)
(Volume) Dilution (ml)
Volume of sample solution to be distilled (ml)
Factor F

0 – 5
10
500
100
0.14

5 – 10
10
500
50
0.28

10 – 15
7
500
50
0.40

15 – 20
5
500
50
0.56

20 – 40
7
500
50
1.00

Variant (c), —
Approximate maximum quantity of nitrogen to be distilled = 200 mg

Sulfuric acid 0.25 M to be placed in the receiving flask = 35 ml

Titration with sodium or potassium hydroxide, 0.5 M solution

Declaration N%
Amount to be weighed (g)
(Volume) Dilution (ml)
Volume of sample solution to be distilled (ml)
Factor F

0 – 5
10
500
200
0.175

5 – 10
10
500
100
0.350

10 – 15
7
500
100
0.500

15 – 20
5
500
100
0.700

20 – 40
5
500
50
1.400

3a.DETERMINATION OF NITRIC AND AMMONIACAL NITROGEN — ULSCH METHOD

SCOPE

1.  This method is for the determination of nitric and ammoniacal nitrogen with reduction according to Ulsch.

FIELD OF APPLICATION

2.  All nitrogenous fertilisers, including compound fertilisers, in which nitrogen is found exclusively in nitrate form, or in ammoniacal and nitrate form.

PRINCIPLE

3.  Reduction of nitrates and nitrites to ammonia by means of metallic iron in an acidic medium and displacement of the ammonia thus formed by the addition of an excess of sodium hydroxide: distillation of the ammonia and determination of the ammonia absorbed in a known volume of standard sulfuric acid solution. Titration of the excess sulfuric acid with a standard solution of sodium or potassium hydroxide.

4.    REAGENTS

4.1
Hydrochloric acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid (p=1.18 g/ml) with an equal volume of water.

4.2
Sulfuric acid, 0.05 M solution.

4.3
Sodium or potassium hydroxide, 0.1 M solution, carbonate free.

4.4
Sulfuric acid solution, approximately 30% H2SO4 (W/V), ammonia free.

4.5
Powdered iron reduced in hydrogen. (The prescribed quantity of iron must be able to reduce at least 0.05 g nitrate nitrogen.)

4.6
Sodium hydroxide solution, 30 g per 100 ml, ammonia free.

4.7
Indicator solutions:

4.7.1 Mixed indicator:

Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water.

Solution B: dissolve 1 g methylene blue in water and make up to 1 litre.

Mix 1 volume of solution A and 2 volumes of solution B.

This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution; use 0.5 ml (10 drops).

4.7.2 Methyl red indicator solution:

Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and filter if necessary.

This indicator may be used (4 – 5 drops) instead of the preceding one.

4.8
Anti-bump granules of pumice stone, washed in hydrochloric acid and ignited.

4.9
Sodium nitrate.

APPARATUS

5.  See Method 2.

6.    PREPARATION OF SAMPLE

See Method 1.

7.    PROCEDURE

Preparation of the solution

7.1  See Method 2.

Determination

7.2  Place in the receiving flask an exactly measured quantity of standard sulfuric acid (4.2) as indicated in the Table of Method 2 (variant (a)) and add the appropriate quantity of indicator solution (4.7.1 or 4.7.2).

The end of the extension tube of the condenser must be below the surface of the standard acid in the receiving flask.

Using a pipette, transfer an aliquot part of the clear solution as indicated in the Table of Method 2 (variant (a)) to the distillation flask of the apparatus. Add 350 ml water, 20 ml 30% sulfuric acid solution (4.4), stir, and add 5 g of reduced iron (4.5). Wash the neck of the flask with several ml of water, and place a small, long-stemmed funnel in the neck of the flask. Heat in a boiling water bath for an hour and then wash the stem of the funnel with a few ml of water. Allow to cool to room temperature.

Taking care to avoid any loss of ammonia, add 50 ml concentrated sodium hydroxide solution (4.6) to the contents of the distillation flask, or in the cases where 20 ml of hydrochloric acid (4.1) has been used to dissolve the sample, add 60 ml of concentrated sodium hydroxide solution (4.6). Assemble the distillation apparatus. Distil the ammonia according to the procedure given in Method 2. Titrate the excess acid with the standard solution of sodium or potassium hydroxide (4.3).

Blank test

7.3  Carry out a blank test (omitting only the sample) under the same conditions and allow for this in the calculation of the final result.

Control test

7.4  Before analysis check that the apparatus is working properly and that the correct application of the method is used by taking an aliquot portion of a freshly prepared solution of sodium nitrate (4.9) containing 0.045 g to 0.05 g of nitrogen.

EXPRESSION OF RESULTS

8.  Express the results of analysis as a percentage of nitric nitrogen, or combined ammoniacal and nitric nitrogen, contained in the fertiliser as received for analysis.

3b.DETERMINATION OF NITRIC AND AMMONIACAL NITROGEN — ARND METHOD

SCOPE

1.  This method is for the determination of nitric and ammoniacal nitrogen with reduction according to Arnd (modified for each of the variants (a), (b) and (c)).

FIELD OF APPLICATION

2.  See Method 3a.

PRINCIPLE

3.  Reduction of nitrates and nitrites to ammonia in a neutral aqueous solution by means of a metallic alloy composed of 60% Cu and 40% Mg (Arnd’s alloy) in the presence of magnesium chloride.

Distillation of the ammonia and absorption in a known volume of standard sulfuric acid solution. Titration of the excess acid with a standard solution of sodium or potassium hydroxide.

4.    REAGENTS

4.1
Hydrochloric acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid (p=1.18 g/ml) with an equal volume of water.

4.2
Sulfuric acid, 0.05 M solution
for variant (a) (see page16)

4.3
Sodium or potassium hydroxide, 0.1 M solution, carbonate free

4.4
Sulfuric acid, 0.1 M solution
for variant (b) (see page 16)

4.5
Sodium or potassium hydroxide, 0.2 M solution, carbonate free

4.6
Sulfuric acid, 0.25 M solution
for variant (c) (see page 16)

4.7
Sodium or potassium hydroxide, 0.5 M solution, carbonate free

4.8
Sodium hydroxide solution, approximately 2 M.

4.9
Arnd’s alloy — powdered to pass through a sieve with square apertures less than 1.00 mm.

4.10

Magnesium chloride solution, 20% (W/V):Dissolve 200 g magnesium chloride (MgCl2.6H2O) in approximately 600 – 700 ml water in a one litre flat bottomed flask. To prevent frothing, add 15 g magnesium sulfate (MgSO4.7H2O). After dissolution add 2 g magnesium oxide and a few anti-bump granules of pumice stone and concentrate the suspension to 200 ml by boiling, thus expelling any trace of ammonia from the reagents. Cool, make up the volume to 1 litre and filter.

4.11
Indicator solutions:

4.11.1 Mixed indicator:

Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water.

Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of A with 2 volumes of B.

This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops).

4.11.2 Methyl red indicator solution:

Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and filter if necessary. This indicator may be used (4 to 5 drops) instead of the preceding one.

4.11.3 Congo red indicator solution:

Dissolve 3 g Congo red in 1 litre warm water and filter if necessary after cooling. This indicator may be used, instead of the two described above, in the neutralisation of acid extracts before distillation, using 0.5 ml per 100 ml of liquid to be neutralised.

4.12
Anti-bump granules of pumice stone washed in hydrochloric acid and ignited.

4.13
Sodium nitrate.

APPARATUS

5.  See Method 2.

PREPARATION OF SAMPLE

6.  See Method 1.

7.    PROCEDURE

Preparation of the solution for analysis

7.1  See Method 2.

Determination

7.2  According to the chosen variant, place in the receiving flask a measured quantity of standard sulfuric acid as indicated in the Table of Method 2. Add the appropriate quantity of chosen indicator solution (4.11.1 or 4.11.2) and if necessary water to give a volume of a least 50 ml. The end of the extension tube of the condenser must be below the surface of the solution.

Using a pipette, take, according to the Table, an aliquot part of the clear solution and place in the distillation flask. Add sufficient water to obtain a total volume of about 350 ml (see Note), 10 g Arnd’s alloy (4.8), 50 ml magnesium chloride solution (4.10) and a few fragments of pumice stone (4.12). Rapidly connect the flask to the distillation apparatus. Heat gently for about 30 minutes. Then increase the heating to distil the ammonia. Continue the distillation for about an hour.

After this time, the residue in the flask ought to have a syrupy consistency. When the distillation has finished, titrate the quantity of excess acid in the receiving flask according to the procedure in Method 2.

Note:When the sample solution is acidic (addition of 20 ml hydrochloric acid (4.1) to dissolve the sample) the aliquot part taken for analysis is neutralised in the following way: to the distillation flask containing the aliquot part add about 250 ml water, the necessary quantity of one of the indicators (4.11.1, 4.11.2, 4.11.3) and swirl or mix carefully. Neutralise with 2 M sodium hydroxide solution (4.8) and acidify again with a drop of hydrochloric acid (4.1). Then proceed as indicated in 7.2.

Blank test

7.3  Carry out a blank test under the same conditions (omitting only the samples) and allow for this in the calculation of the final result.

Control test

7.4  Before analysis, check that the apparatus is working properly and that the correct technique is applied using a freshly prepared solution of sodium nitrate (4.13) containing 0.050 g to 0.150 g nitrogen depending on the variant chosen.

EXPRESSION OF RESULTS

8.  Express the results of the analysis as a percentage of nitric nitrogen, or combined ammoniacal and nitric nitrogen, contained in the fertiliser as received for analysis.

3c.DETERMINATION OF NITRIC AND AMMONIACAL NITROGEN — DEVARDA METHOD

SCOPE

1.  This method is for the determination of nitric and ammoniacal nitrogen with reduction according to Devarda (modified for each of the variants (a), (b) and (c)).

FIELD OF APPLICATION

2.  See Method 3a.

PRINCIPLE

3.  Reduction of nitrates and nitrites to ammonia in a strongly alkaline solution by means of a metallic alloy composed of 45% A1, 5% Zn and 50% Cu (Devarda’s alloy). Distillation of the ammonia and absorption in a known volume of standard sulfuric acid; titration of the excess sulfuric acid with a standard solution of sodium or potassium hydroxide.

4.    REAGENTS

4.1
Hydrochloric acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid (p=1.18 g/ml) with an equal volume of water.

4.2
Sulfuric acid, 0.05 M solution
for variant (a) (see page 16)

4.3
Sodium or potassium hydroxide, 0.1 M solution, carbonate free

4.4
Sulfuric acid, 0.1 M solution
for variant (b) (see page 16)

4.5
Sodium or potassium hydroxide, 0.2 M solution, carbonate free

4.6
Sulfuric acid, 0.25 M solution
for variant (c) (see page 16)

4.7
Sodium or potassium hydroxide, 0.5 M solution, carbonate free

4.8
Devarda’s alloy — powdered so that 90 to 100% will pass through a sieve with apertures less than 0.25 mm square, 50 to 75% will pass through a sieve with apertures of less than 0.075 mm square. (Pre-packed bottles containing a maximum of 100 g are recommended.)

4.9
Sodium hydroxide solution, 30 g per 100 ml, ammonia free.

4.10
Indicator solutions:

4.10.1 Mixed indicator:

Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water.

Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of A with 2 volumes of B.

This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops).

4.10.2 Methyl red indicator:

Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and filter if necessary. This indicator (4 to 5 drops) may be used instead of the preceding one.

4.11
Ethanol, 95%.

4.12
Sodium nitrate.

5.    APPARATUS

Distillation apparatus consisting of a round bottomed flask of suitable capacity, connected to a condenser by means of a splash head, equipped, in addition, with a bubble trap on the receiving flask to prevent any loss of ammonia.

An example of the type of apparatus recommended for this determination is reproduced in Figure 5 in the Appendix.

PREPARATION OF THE SAMPLE

6.  See Method 1.

7.    PROCEDURE

Preparation of the solution for analysis

7.1  See Method 2.

Determination

7.2  According to the variant chosen, place in the receiving flask an exactly measured quantity of standard sulfuric acid as indicated in the Table. Add the appropriate quantity of the chosen indicator solution (4.10.1 or 4.10.2) and sufficient water to give a volume of 50 ml. The end of the extension tube of the condenser must be below the surface of the solution. Fill the bubble trap with distilled water.

Using a pipette, take an aliquot part of the clear solution as indicated in the Table and place in the distillation flask. Add sufficient water to the distillation flask to obtain a volume of 250 – 300 ml, then add 5 ml ethanol (4.11) and 4 g Devarda’s alloy (4.8).

Note:In the presence of calcium salts such as calcium nitrate and calcium ammonium nitrate, it is necessary to add 0.7 g disodium hydrogen phosphate (Na2HPO4.2H2O) before distillation for each gram of sample present in the aliquot part, to prevent the formation of calcium hydroxide.

Taking the necessary precautions to avoid loss of ammonia, add to the flask about 30 ml of 30% sodium hydroxide solution (4.9) and finally, in the case of acid-soluble samples, an additional quantity sufficient to neutralise the quantity of hydrochloric acid (4.1) present in the aliquot part taken for the analysis. Connect the distillation flask to the apparatus, ensuring the tightness of connections. Carefully swirl the flask to mix the contents.

Warm gently, so that the release of hydrogen decreases appreciably over about half an hour and the liquid begins to boil. Continue the distillation, increasing the heat so that at least 200 ml of liquid distils in about 30 minutes. (Do not prolong the distillation beyond 45 minutes.)

When the distillation is complete, disconnect the receiving flask from the apparatus, carefully wash the extension tube and bubble trap, collecting the rinsings in the titration flask. Titrate the excess acid according to the procedure in Method 2.

Blank test

7.3  Carry out a blank test under the same conditions omitting only the sample and allow for this in the calculation of the final results.

Control test

7.4  Before carrying out the analysis, check that the apparatus is working properly and that the correct application of the method is used, by taking an aliquot portion of a freshly prepared solution of sodium nitrate (4.12) containing, according to the variant chosen, 0.050 g to 0.150 g.

EXPRESSION OF RESULTS

8.  Express the results of analysis as a percentage of nitric nitrogen, or combined ammoniacal and nitric nitrogen, contained in the fertiliser as received for analysis.

4a.DETERMINATION OF TOTAL NITROGEN IN CALCIUM CYANAMIDE — IN THE ABSENCE OF NITRATE

SCOPE

1.  This method is for the determination of total nitrogen in nitrate-free calcium cyanamide.

FIELD OF APPLICATION

2.  Exclusively to calcium cyanamide (nitrate free).

PRINCIPLE

3.  After digestion using the Kjeldahl method, the ammoniacal nitrogen formed is displaced by sodium hydroxide and collected in a standard solution of sulfuric acid. The excess sulfuric acid is titrated with a standard solution of sodium or potassium hydroxide.

4.    REAGENTS

4.1
Sulfuric acid solution 50% (V/V): dilute an appropriate volume of sulfuric acid (p=1.84 g/ml) with an equal volume of water.

4.2
Potassium sulfate.

4.3
Copper oxide (CuO), 0.3 – 0.4 g for each determination or an equivalent quantity of copper sulfate pentahydrate (0.95 to 1.25g) for each determination.

4.4
Sodium hydroxide solution 30g per 100 ml, ammonia free.

4.5
Sulfuric acid, 0.05 M solution
for variant (a) (see page 16)

4.6
Sodium or potassium hydroxide, 0.1 M solution, carbonate free

4.7
Sulfuric acid, 0.1 M solution
for variant (b) (see page 16)

4.8
Sodium or potassium hydroxide, 0.2 M solution, carbonate free

4.9
Sulfuric acid, 0.25 M solution
for variant (c) (see page 16)

4.10
Sodium or potassium hydroxide, 0.5 M solution, carbonate free

4.11
Indicator solutions:

4.11.1 Mixed indicator:

Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water.

Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of A with 2 volumes of B.

This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops).

4.11.2 Methyl red indicator:

Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and filter if necessary. This indicator (4 to 5 drops) may be used instead of the preceding one.

4.12
Anti-bump granules of pumice stone, washed in hydrochloric acid and ignited.

4.13
Potassium thiocyanate.

5.    APPARATUS

Distillation apparatus. See Method 2.

PREPARATION OF SAMPLE

6.  See Method 1.

7.    PROCEDURE

Preparation of the solution

7.1  Weigh to the nearest 0.001 g, 1 g of the prepared sample and place it in the Kjeldahl flask. Add 50 ml 50% sulfuric acid (4.1), 10-15 g potassium sulfate (4.2) and one of the prescribed catalysts (4.3). Heat slowly to drive off the water, boil gently for two hours, allow to cool, and dilute with 100-150 ml water.

Cool again, transfer the suspension quantitatively to a 250 ml graduated flask, make up to volume with water, shake and filter through a dry filter into a dry flask. Discard the first portion of the filtrate.

Determination

7.2  According to the variant chosen (see Method 2) transfer with a pipette 50, 100 or 200 ml of the solution to the distillation apparatus and add sufficient sodium hydroxide solution (4.4) to ensure a considerable excess. Distil the ammonia and titrate the excess acid as described in Method 2.

Blank test

7.3  Make a blank test (omitting only the sample) under the same conditions and allow for this in the calculation of the final result.

Control test

7.4  Before carrying out the analysis, check that the apparatus is working properly and that the correct application of the method is used, by taking an aliquot portion of a standard solution of potassium thiocyanate (4.13), approximating to the concentration of nitrogen in the sample.

EXPRESSION OF RESULT

8.  The result of the analysis must be expressed as the percentage of nitrogen (N) contained in the fertiliser as received for analysis.

Variant (a): N%=(50 – A) × 0.7

Variant (b): N%=(50 – A) × 0.7

Variant (c): N%=(35 – A) × 0.875

Where A = millilitres of sodium or potassium hydroxide used for the titration.

4b.DETERMINATION OF TOTAL NITROGEN IN CALCIUM CYANAMIDE — IN THE PRESENCE OF NITRATE

SCOPE

1.  This method is for the determination of total nitrogen in calcium cyanamide.

FIELD OF APPLICATION

2.  The method is applicable to calcium cyanamide containing nitrates.

PRINCIPLE

3.  The direct application of Kjeldahl’s method cannot be applied to calcium cyanamides containing nitrates. For this reason the nitric nitrogen is reduced to ammonia with metallic iron and stannous chloride before Kjeldahl digestion. The ammoniacal nitrogen is then determined as in Method 4a.

4.    REAGENTS

4.1
Sulfuric acid (p=1.84 pg/ml).

4.2
Powdered iron reduced in hydrogen.

4.3
Potassium sulfate, finely pulverised.

4.4
Sulfuric acid, 0.05 M solution
for variant (a) (see page 16)

4.5
Sodium or potassium hydroxide, 0.1 M solution, carbonate free

4.6
Sulfuric acid, 0.1 M solution
for variant (b) (see page16)

4.7
Sodium or potassium hydroxide, 0.2 M solution, carbonate free

4.8
Sulfuric acid, 0.25 M solution
for variant (c) (see page 16)

4.9
Sodium or potassium hydroxide, 0.5 M solution, carbonate free

4.10
Indicator solutions:

4.10.1 Mixed indicator:

Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water.

Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of A with 2 volumes of B.

This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops) of this indicator solution.

4.10.2 Methyl red indicator: Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and filter if necessary. This indicator (4 to 5 drops) may be used instead of the preceding one.

4.11
Solution of stannous chloride:

Dissolve 120 g of stannous chloride (SnCl2.2H2O) in 400 ml concentrated hydrochloric acid (p=1.18 g/ml) and make up to 1 litre with water. The solution must be completely clear and prepared immediately before use.
It is essential to check the reducing power of the stannous chloride. Dissolve 0.5 g of stannous chloride in 2 ml concentrated hydrochloric acid (p=1.18 g/ml) and make up to 50 ml with water. Then add 5 g of Rochelle salt (potassium sodium tartrate) and a sufficient quantity of sodium bicarbonate for the solution to show an alkaline reaction to a litmus paper test.
Titrate with 0.1 M iodine solution in the presence of a starch solution as an indicator.
1 ml of 0.1 M iodine solution corresponds to 0.01128 g SnCl2.2H2O.
At least 80% of the total tin present in the solution thus prepared must be in the bivalent form. For the titration at least 35 ml of 0.1 M iodine solution should be used.

4.12
Sodium hydroxide solution, 30 g per 100 ml, ammonia free.

4.13
Standard nitrate-ammoniacal solution:

Weigh out 2.500 g of potassium nitrate and 10.160 g of ammonium sulfate into a 250 ml graduated flask. Dissolve in water and make up to 250 ml. 1 ml of this solution contains 0.010 g of nitrogen.

4.14
Anti-bump granules of pumice stone, washed in hydrochloric acid and ignited.

APPARATUS

5.  Distillation apparatus. See Method 2.

PREPARATION OF THE SAMPLE

6.  See Method 1.

7.    PROCEDURE

Preparation of the solution

7.1  Weigh to the nearest 0.001 g,1 g of the prepared sample into the Kjeldahl flask. Add 0.5 g of powdered iron (4.2) and 50 ml of the stannous chloride solution (4.11), stir and leave standing for half an hour. During the time it is left standing, stir again after 10 and 20 minutes. Then add 10 g of potassium sulfate (4.3) and 30 ml of sulfuric acid (4.1). Boil and continue for an hour after the appearance of white fumes. Leave to cool and dilute with 100-150 ml of water. Transfer the suspension quantitatively into a 250 ml graduated flask, cool and make up to volume with water, mix and filter through a dry paper into a dry container. Discard the first portion of the filtrate.

Determination

7.2  According to the variant chosen (see Method 2) transfer with a pipette 50, 100 or 200 ml of the solution to the distillation apparatus and add sufficient sodium hydroxide solution (4.12) to ensure a considerable excess. Distil the ammonia and titrate the excess acid as described in Method 2.

Blank test

7.3  Make a blank test (omitting only the sample) under the same conditions and allow for this in the calculation of the final result.

Control test

7.4  Before carrying out the analysis, check that the apparatus is working properly and that the correct application of the method is used with a standard solution containing quantities of ammoniacal and nitrate nitrogen comparable to the quantities of cyanamide and nitrate nitrogen contained in nitrated calcium cyanamide.

EXPRESSION OF RESULT

8.  The result of the analysis must be expressed as the percentage of total nitrogen (N) contained in the fertiliser as received for analysis.

Variant (a): N%=(50 – A) × 0.7

Variant (b): N%=(50 – A) × 0.7

Variant (c): N%=(35 – A) × 0.875

Where A = millilitres of sodium or potassium hydroxide used for the titration.

5.DETERMINATION OF TOTAL NITROGEN IN UREA

SCOPE

1.  This method is for the determination of total nitrogen in urea.

FIELD OF APPLICATION

2.  The method is applicable exclusively to urea fertilisers which are nitrate free.

PRINCIPLE

3.  Urea is transformed quantitatively into ammonia by boiling in the presence of sulfuric acid. The ammonia thus obtained is distilled from an alkaline medium and collected in an excess of standard sulfuric acid. The excess acid is titrated by means of a standard alkaline solution.

4.    REAGENTS

4.1
Sulfuric acid, concentrated (p = 1.84 g/ml).

4.2
Sodium hydroxide solution, 30 g per 100 ml, ammonia free.

4.3
Sulfuric acid, 0.05 M solution
for variant (a) (see page 16)

4.4
Sodium or potassium hydroxide, 0.1 M solution, carbonate free

4.5
Sulfuric acid, 0.1 M solution
for variant (b) (see page 16)

4.6
Sodium or potassium hydroxide, 0.2 M solution, carbonate free

4.7
Sulfuric acid, 0.25 M solution
for variant (c) (see page 16)

4.8
Sodium or potassium hydroxide, 0.5 M solution, carbonate free

4.9
Indicator solutions:

4.9.1 Mixed indicator:

Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water.

Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of A with 2 volumes of B.

This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops).

4.9.2 Methyl red indicator:

Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water. Filter if necessary. This indicator (4 to 5 drops) may be used instead of the preceding one.

4.10
Anti-bump granules of pumice stone, washed in hydrochloric acid and ignited.

4.11
Urea.

5.    APPARATUS

Distillation apparatus. See Method 2.

PREPARATION OF THE SAMPLE

6.  See Method 1.

7.    PROCEDURE

Preparation of the solution

7.1  Weigh to the nearest 0.001 g, 2.5 g of the prepared sample into a 300 ml Kjeldahl flask and moisten with 20 ml water. Add with care 20 ml concentrated sulfuric acid (4.1) and a few anti-bump granules (4.10). To prevent splashing, place a long-stemmed glass funnel in the neck of the flask. Heat slowly at first, then increase the heat until white fumes are observed (30 – 40 minutes).

Cool and dilute with 100 – 150 ml water. Transfer quantitatively to a 500 ml graduated flask, discarding any sediment. Allow to cool to room temperature. Make up to volume with water, mix and, if necessary, filter through a dry paper into a dry receptacle. Discard the first portion of the filtrate.

Determination

7.2  According to the variant chosen (see Method 2) transfer with a pipette 25, 50 or 100 ml of the solution to the distillation apparatus and add sufficient sodium hydroxide solution (4.2) to ensure a considerable excess. Distil the ammonia and titrate the excess acid as described in Method 2.

Blank test

7.3  Carry out a blank test (omitting only the sample) under the same conditions and allow for this in the calculation of the final result.

Control test

7.4  Before carrying out the analysis, check that the apparatus is working properly and that the correct application of the method is used, with an aliquot portion of a freshly prepared solution of urea (4.11).

EXPRESSION OF RESULT

8.  Express the result as the percentage of total nitrogen (N) contained in the fertiliser as received for analysis.

Variant (a): N%=(50 – A) × 1.12

Variant (b): N%=(50 – A) × 1.12

Variant (c): N%=(35 – A) × 1.40

Where A = millilitres of sodium or potassium hydroxide used for the titration.

6.DETERMINATION OF CYANAMIDE NITROGEN

SCOPE

1.  This method is for the determination of cyanamide nitrogen.

FIELD OF APPLICATION

2.  Calcium cyanamide and calcium cyanamide/nitrate mixtures.

PRINCIPLE

3.  Cyanamide nitrogen is precipitated as a silver complex and estimated in the precipitate by Kjeldahl’s method.

4.    REAGENTS

4.1
Glacial acetic acid.

4.2
Ammonia solution: dilute one volume of ammonia (p=0.88 pg/ml) with 3 volumes of water.p

4.3
Ammoniacal silver solution, according to Tollens, freshly prepared: mix 500 ml silver nitrate solution (10 g per 100 ml) with 500 ml ammonia solution (4.2).

Do not expose unnecessarily to light, heat or air.
Safety precaution: when handling ammoniacal silver nitrate solution, safety goggles must be worn.

4.4
Concentrated sulfuric acid (p=1.84 g/ml).

4.5
Potassium sulfate.

4.6
Copper oxide (CuO), 0.3 – 0.4 g for each determination or an equivalent quantity of copper sulfate pentahydrate (0.95 – 1.25 g) for each determination.

4.7
Sodium hydroxide solution, 30 g per 100 ml, ammonia free.

4.8
Sulfuric acid, 0.05 M solution.

4.9
Sodium or potassium hydroxide, 0.1 M solution.

4.10
Indicator solutions:

4.10.1 Mixed indicator:

Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water.

Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of A with 2 volumes of solution B.

This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops).

4.10.2 Methyl red indicator:

Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water. Filter if necessary. This indicator (4 to 5 drops) may be used instead of the preceding one.

4.11
Anti-bump granules of pumice stone, washed in hydrochloric acid and ignited.

4.12
Potassium thiocyanate.

5.    APPARATUS

Distillation apparatus. See Method 2.

500 ml graduated flask (e.g. Stohmann).

Rotary shaker, 35 – 40 turns per minute.

PREPARATION OF THE SAMPLE

6.  See Method 1.

7.    PROCEDURE

Preparation of the solution for analysis

7.1  Weigh, to the nearest 0.001 g, 2.5 g of the prepared sample into a small glass mortar. Grind the sample three times with water, pouring off the water after each grinding into the 500 ml graduated flask (5.2). Transfer the sample quantitatively into the flask, washing the mortar, pestle and funnel with water. Make up with water to approximately 400 ml. Add 15 ml acetic acid (4.1). Shake on the rotary shaker (5.3) for two hours.

Make up to 500 ml with water, mix and filter. Discard the first portion of the filtrate.

Proceed immediately to 7.2.

Determination

7.2  Transfer 50.0 ml of the filtrate to a 250 ml beaker. Add ammonia solution (4.2) until slightly alkaline and add 30 ml warm ammoniacal silver nitrate (4.3) to precipitate the yellow silver complex of cyanamide. Leave overnight, filter and wash the precipitate with cold water until completely free of ammonia.

Place the filter paper and the precipitate, still moist, in a Kjeldahl flask, add 10 – 15 g potassium sulfate (4.5), the catalyst (4.6) in the prescribed proportion, then 50 ml water and 25 ml concentrated sulfuric acid (4.4). Warm the flask slowly, whilst shaking it gently until the contents come to the boil. Increase the heat, boil until the contents of the flask become either colourless or pale green. Continue boiling for one hour, then leave to cool.

Transfer the liquid quantitatively from the Kjeldahl flask to the distillation flask, add a few anti-bump granules of pumice stone (4.11) and make up with water to a total volume of approximately 350 ml. Mix and cool. Add sufficient sodium hydroxide solution (4.7) to ensure a considerable excess.

Distil the ammonia and titrate the excess acid as described in Method 2 (variant (a)).

Blank test

7.3  Make a blank test (omitting only the sample) under the same conditions and allow for this in the calculation of the final result.

Control test

7.4  Before carrying out the analysis, check that the apparatus is working properly and that the correct application of the method is used, with an aliquot portion of a standard solution of potassium thiocyanate (4.12), corresponding to 0.05 g of nitrogen.

EXPRESSION OF RESULT

8.  Express the result as the percentage of cyanamide nitrogen contained in the fertiliser as received for analysis.

N%=(50 – A) × 0.56

Where A = millilitres of sodium or potassium hydroxide used for the titration.

7.DETERMINATION OF BIURET IN UREA

1.    SCOPE

This method is for the determination of biuret in urea.

2.    FIELD OF APPLICATION

The method is applied exclusively to urea.

3.    PRINCIPLE

In an alkaline medium, in the presence of potassium sodium tartrate, biuret and bivalent copper form a violet cupric compound, the absorbance of which is measured at 546 nm.

4.    REAGENTS

4.1
Methanol.

4.2
Sulfuric acid solution, approximately 0.05 M.

4.3
Sodium hydroxide solution, approximately 0.1 M.

4.4
Alkaline solution of potassium sodium tartrate:

In a 1 litre graduated flask dissolve 40 g of sodium hydroxide in 500 ml of water and leave to cool. Add 50 g of potassium sodium tartrate (KNaC4H4O6.4H2O). Make up to the mark and mix. Leave standing 24 hours before use.

4.5
Copper sulfate solution:

In a 1 litre graduated flask dissolve 15 g of copper sulfate (CuSO4.5H2O) in 500 ml of water. Make up to the mark and mix.

4.6
Biuret standard solution:

In a 250 ml graduated flask, dissolve 0.250 g of pure biuret(8) in water. Make up to the mark and mix. 1 ml of this solution contains 0.001 g of biuret. This solution should be freshly prepared.

4.7
Methyl red indicator solution:

Dissolve 0.1 g methyl red in 50 ml 95% ethanol and make up to 100 ml with water. Filter if necessary.

5.    APPARATUS

Spectrophotometer.

6.    PREPARATION OF SAMPLE

See Method 1.

7.    PROCEDURE

Preparation of the standard curve

7.1  Transfer 2, 5, 10, 20, 25 and 50 ml aliquot portions of biuret standard solution (4.6) into a series of six 100 ml graduated flasks. Make up the volumes to about 50 ml with water, add one drop of indicator solution (4.7) and neutralise, if necessary, with 0.05 M sulfuric acid (4.2). Add the swirling 20.0 ml of the alkaline tartrate solution (4.4) and then 20.0 ml copper sulfate solution (4.5). Make up to the mark with water, mix and allow to stand at 30+ 2 C for fifteen minutes.

At the same time prepare a reagent blank as follows. Place 50 ml water in a 100 ml graduated flask and proceed as described above from “… add one drop of indicator solution …”.

Measure the absorbance of each solution at 546 nm against the reagent blank as reference, using cells of suitable path length. Plot the calibration curve, using the absorbances as the ordinates and the corresponding quantities of biuret in milligrams, as the abscissae.

Preparation of solution for analysis

7.2  Weigh to the nearest 0.001g, 10 g of the prepared sample; dissolve in about 150 ml of water in a 250 ml graduated flask and make up to the mark and mix. Filter if necessary.

Note 1:If the sample for analysis contains more than 0.015 g of ammoniacal nitrogen, dissolve in 50 ml methanol (4.1) in a 250 ml beaker. Reduce by evaporation to a volume of about 25 ml. Transfer quantitatively to a graduated 250 ml flask. Make up to the mark with water. Filter, if necessary, through a dry fluted paper into a dry receiver.

Note 2:Elimination of the opalescence: if any colloidal substance is present difficulties may arise during filtration. In that case the solution for analysis is prepared as follows: dissolve the sample in 150 ml of water, add 2 ml 1 M hydrochloric acid, and filter the solution into a 250 ml graduated flask. Wash the filters with water and make up to volume. Continue the process according to the method described in 7.3.

Determination

7.3  According to the presumed biuret content, transfer with a pipette 25 or 50 ml from the solution prepared in 7.2, to a 100 ml graduated flask and neutralise if necessary with 0.05 M sulfuric acid or sodium hydroxide solution (4.2 or 4.3) as required, using methyl red indicator (4.7). Add 20.0 ml of the alkaline solution of potassium sodium tartrate (4.4) and 20.0 ml of the copper solution (4.5). Make up to volume, mix thoroughly and leave standing for 15 minutes at 30 C+2. Measure the absorbance of the solution as described in 7.1.

EXPRESSION OF RESULTS

No math image to display

where:

C = mass, in mg, of biuret read from the standard curve;

V = volume of the aliquot used for the determination.

8a.DETERMINATION OF DIFFERENT FORMS OF NITROGEN IN THE SAME SAMPLE — IN THE PRESENCE OF CYANAMIDE NITROGEN

1.    SCOPE

This method is for the determination of any one form of nitrogen in the presence of any other form.

2.    FIELD OF APPLICATION

Any fertiliser in Group 1(a) of Section A, and Groups 1, 2 and 3 of Section B of the Table in Schedule 1 of the Fertilisers Regulations 1991 containing nitrogen in various forms.

3.    PRINCIPLE

Total soluble and insoluble nitrogen

3.1—3.1.1 In the absence of nitrates, the sample is subjected to direct Kjeldahl digestion.

3.1.2 In the presence of nitrates, the sample is subjected to Kjeldahl digestion after reduction with the aid of metallic iron and stannous chloride. In both cases, the ammonia is determined according to Method 2.

Note:If analysis shows an insoluble nitrogen content of more than 0.5%, it is presumed that the fertiliser contains other forms of insoluble nitrogen not specified for fertilisers covered by the list in paragraph 2.

Forms of soluble nitrogen

3.2  The following are determined from different aliquot parts taken from the same solution of the sample:

3.2.1 Total soluble nitrogen

3.2.1.1In the absence of nitrates, by direct Kjeldahl digestion.

3.2.1.2In the presence of nitrates, by Kjeldahl digestion on an aliquot portion taken from the solution after reduction according to Ulsch, the ammonia being determined in both cases as described in Method 2.

3.2.2 Total soluble nitrogen with the exception of nitric nitrogen, by Kjeldahl digestion after elimination in an acid medium of nitric nitrogen with ferrous sulfate, the ammonia being determined as described in Method 2.

3.2.3 Nitric nitrogen by difference

3.2.3.1In the absence of calcium cyanamide, between (3.2.1.2) and (3.2.2) or between total soluble nitrogen (3.2.1.2) and the sum of ammoniacal nitrogen and ureic nitrogen (3.2.4+3.2.5).

3.2.3.2In the presence of calcium cyanamide, between (3.2.1.2) and (3.2.2) and between (3.2.1.2) and the sum of (3.2.4+3.2.5+3.2.6).

3.2.4 Ammoniacal nitrogen

3.2.4.1Solely in the presence of ammoniacal nitrogen and ammoniacal + nitric nitrogen, by applying Method 2.

3.2.4.2In the presence of ureic nitrogen and/or cyanamide nitrogen, by cold distillation after making slightly alkaline, the ammonia being absorbed in a standard solution of sulfuric acid and determined as described in Method 2.

3.2.5 Ureic nitrogen

Either

3.2.5.1By conversion using urease into ammonia which is titrated with a standard solution of hydrochloric acid,

or:

3.2.5.2By gravimetry with xanthydrol, although biuret will also be precipitated by xanthydrol, this should not give rise to a significant error in the determination since its level is generally low in absolute value in compound fertilisers.

or:

3.2.5.3By difference, according to the following table:

Case
Nitric Nitrogen
Ammoniacal Nitrogen
Cyanamide Nitrogen
Difference

1
Absent
Present
Present
(3.2.1.1)-(3.2.4.2+3.2.6)

2
Present
Present
Present
(3.2.2)-(3.2.4.2+3.2.6)

3
Absent
Present
Absent
(3.2.1.1)-(3.2.4.2)

4
Present
Present
Absent
(3.2.2)-(3.2.4.2)

3.2.6 Cyanamide nitrogen, by precipitation as a silver compound, the nitrogen being estimated in the precipitate by the Kjeldahl method.

4.    REAGENTS

Potassium sulfate.

Iron powder, reduced with hydrogen (the prescribed quantity of iron must be able to reduce at least 50 mg of nitric nitrogen).

Potassium thiocyanate.

Potassium nitrate.

Ammonium sulfate.

Urea.

Sulfuric acid solution: dilute an appropriate volume of sulfuric acid (p=1.84 g/ml) with an equal volume of water.

Sulfuric acid, 0.1 M solution.

Sodium hydroxide solution, 30 g per 100 ml, ammonia free.

Sodium or potassium hydroxide, 0.2 M solution, free from carbonates.

Stannous chloride solution:

Dissolve 120 g of stannous chloride (SnCl2.2H2O) in 400 ml of concentrated hydrochloric acid (p=1.18 g/ml) and make up to 1 litre with water. The solution must be perfectly clear and prepared immediately before use.

It is essential to check the reducing power of the stannous chloride: dissolve 0.5 g of stannous chloride in 2 ml of concentrated hydrochloric acid (p=1.18 g/ml) and make up to 50 ml with water. Then add 5 g of Rochelle salt (potassium sodium tartrate) and a sufficient quantity of sodium bicarbonate for the solution to be alkaline to litmus paper.

Titrate with 0.1 M iodine solution in the presence of a starch solution as an indicator.

1 ml of 0.1 M iodine solution corresponds to 0.01128 g of SnCl2.2H2O.

At least 80% of the total tin present in the solution thus prepared must be in bivalent form. For the titration, at least 35 ml of 0.1 M iodine solution must therefore be used.

Sulfuric acid, concentrated (p=1.84 g/ml).

Hydrochloric acid solution: dilute an appropriate volume of hydrochloric acid (p=1.18 g/ml) with an equal volume of water.

Glacial acetic acids.

Sulfuric acid solution, approximately 30% (W/V) H2SO4.

Ferrous sulfate, crystalline, FeSO4.7H2O

Sulfuric acid, 0.05 M solution.

Octan-1-ol.

Potassium carbonate, saturated solution.

Sodium or potassium hydroxide, 0.1 M solution, free from carbonate.

Barium hydroxide, saturated solution.

Sodium carbonate solution, 10 g per 100 ml.

Hydrochloric acid, 2 M solution.

Hydrochloric acid, 0.1 M solution.

Urease solution: Suspend 0.5 g of active urease in 100 ml of distilled water. Using 0.1 M hydrochloric acid (4.24), adjust the pH to 5.4, measured by pH meter.

Xanthydrol solution, 5 g per 100 ml in ethanol or methanol (4.31) (do not use products giving a high proportion of insoluble matter). The solution may be kept for three months in a well-stoppered bottle, away from the light.

Copper oxide (CuO): 0.3 to 0.4 g per determination or an equivalent quantity of copper sulfate pentahydrate (0.95 to 1.25 g) per determination.

Anti-bump granules washed in hydrochloric acid and ignited.

Indicator solutions:

4.29.1 Mixed indicator solution: Solution A: dissolve 1 g of methyl red in 37 ml of 0.1 M sodium hydroxide solution and make up to one litre with water. Solution B: dissolve 1 g of methylene blue in water and make up to one litre. Mix one volume of solution A and 2 volumes of solution B. This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0.5 ml (10 drops) of this indicator solution.

4.29.2 Methyl red indicator solution: Dissolve 0.1 g of methyl red in 50 ml of 95% ethanol, make up to 100 ml with water and filter if necessary. This indicator (4 to 5 drops) can be used instead of the previous one.

Indicator papers: Litmus, bromothymol blue (or other papers sensitive in the range pH 6 to 8).

Ethanol or methanol: solution 95%.

5.    APPARATUS

Distillation apparatus. See Method 2.

Apparatus for the determination of ammoniacal nitrogen 7.2.5.3. An example of the recommended apparatus is reproduced in Figure 6 in the Appendix.

The apparatus is made up of a specially shaped receptacle with a ground glass neck, a side neck, a connecting tube with a splash head and a perpendicular tube for the introduction of air. The tubes can be connected to the receptacle by means of a simple perforated rubber bung. It is important to give a suitable shape to the end of the tubes introducing air, since the bubbles of gas must be evenly distributed throughout the solutions contained in the receptacle and the absorber. The best arrangement consists of small mushroom-shaped pieces with an external diameter of 20 mm and six openings of 1 mm around the periphery.

Apparatus for the estimation of urea nitrogen (7.2.6.1).

It consists of a 300 ml Erlenmeyer flask, with a separating funnel and a small absorber. An example of the recommended apparatus is reproduced in Figure 7 in the Appendix.

Rotary shaker, 35 – 40 turns per minute.

pH meter.

Laboratory oven.

Sintered glass crucibles, diameter of pores 5 to 15 microns.

6.    PREPARATION OF THE SAMPLE

See Method 1.

7.    PROCEDURE

Total soluble and insoluble nitrogen

7.1—7.1.1 In the absence of nitrate

7.1.1.1Digestion

Weigh to the nearest 0.001 g, a quantity of the prepared sample containing not more than 100 mg of nitrogen. Place in the flask of the distillation apparatus (5.1). Add 10 to 15 g of potassium sulfate (4.1), the prescribed quantity of catalyst (4.27), and a few anti-bump granules (4.28). Then add 50 ml of dilute sulfuric acid (4.7), and mix thoroughly. First heat gently, mixing from time to time, until foaming ceases. Then heat so that the liquid boils steadily and keep it boiling for one hour after the solution has become clear, preventing any organic matter from sticking to the sides of the flask. Allow to cool. Carefully add about 350 ml of water, with mixing. Ensure that the dissolution is as complete as possible. Allow to cool and connect the flask to the distillation apparatus (5.1).

7.1.1.2Distillation of ammonia

Transfer with a pipette 50 ml of standard 0.1 M sulfuric acid (4.8) into the receiver of the apparatus. Add the indicator (4.29.1 or 4.29.2). Ensure that the tip of the condenser is at least 1 cm below the level of the solution.

Taking the necessary precautions to avoid any loss of ammonia, carefully add to the distillation flask enough of the concentrated sodium hydroxide solution (4.9) to make the liquid strongly alkaline (120 ml is generally sufficient: check by adding a few drops of phenolphthalein. At the end of the distillation the solution in the flask must still be clearly alkaline). Adjust the heating of the flask so as to distil 150 ml in half an hour. Test with indicator paper (4.30) that the distillation has been completed. If it has not, distil a further 50 ml and repeat the test until the supplementary distillate reacts neutrally to the indicator paper (4.30). Then lower the receiver, distil a few ml more and rinse the tip of the condenser. Titrate the excess acid with a standard solution of potassium or sodium hydroxide 0.2 M (4.10) to the end point of the indicator.

7.1.1.3Blank test

Make a blank test under the same conditions (omitting only the sample) and use this value in the calculation of the final result.

7.1.14 Expression of the result

No math image to display

where:

a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the blank.

A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the analysis.

M = mass of the sample in grams.

7.1.2 In the presence of nitrate

7.1.2.1Test sample

Weigh to the nearest 0.001g, a quantity of the sample containing not more than 40 mg of nitric nitrogen.

7.1.2.2Reduction of the nitrate

Mix the sample in a small mortar with 50 ml of water. Transfer with the minimum amount of distilled water into a 500 ml Kjeldahl flask. Add 5 g of reduced iron (4.2) and 50 ml of stannous chloride solution (4.11). Shake and leave to stand for half an hour. During this time shake again after 10 and 20 minutes.

7.1.2.3Kjeldahl digestion

Add 30 ml of sulfuric acid (4.12), 5 g of potassium sulfate (4.1), the prescribed quantity of catalyst (4.27) and some anti-bump granules (4.28). Heat gently with the flask slightly tilted. Increase the heat slowly and swirl the solution frequently to keep the mixture suspended; the liquid darkens and then clears with the formation of a yellow-green anhydrous iron sulfate suspension. After obtaining a clear solution simmer for one hour. Leave to cool. Cautiously take up the contents of the flask in a little water and add little by little 100 ml of water. Mix and transfer the contents of the flask into a 500 ml graduated flask. Rinse the flask several times with distilled water. Make up the volume with water and mix. Filter through a dry paper into a dry receiver. Discard the first portion of the filtrate.

7.1.2.4Distillation of ammonia

Transfer into the flask of the distillation apparatus (5.1), an aliquot part containing not more than 100 mg of nitrogen. Dilute to about 350 ml with distilled water, add a few anti-bump granules (4.28), connect the flask to the distillation apparatus and continue the determination as described in paragraph 7.1.1.2.

7.1.2.5Blank test

See 7.1.1.3.

7.1.2.6Expression of the result

No math image to display

where:

a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the blank.

A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the analysis.

M = mass of the sample, expressed in grams, present in the aliquot part taken for a analysis.

Forms of soluble nitrogen

7.2—7.2.1 Preparation of the solution to be analysed

Weigh to the nearest 0.001 g, 10 g of the sample and place it in a 500 ml graduated flask.

7.2.1.1In the case of fertilisers not containing cyanamide nitrogen

Add to the flask 50 ml of water and then 20 ml of dilute hydrochloric acid (4.13). Shake and leave it to stand until the evolution of carbon dioxide ceases. Then add 400 ml of water and shake for half an hour on the rotary shaker (5.4).

Make up to the volume with water, mix and filter through a dry filter into a dry receiver. Discard the first portion of the filtrate.

7.2.1.2In the case of fertilisers containing cyanamide nitrogen

Add to the flask 400 ml of water and a few drops of methyl red (4.29.2). If necessary make the solution acidic by using acetic acid (4.14). Add 15 ml of acetic acid (4.14). Shake on the rotary shaker (5.4) for 2 hours. If necessary, re-acidify the solution during the operation, using acetic acid (4.14). Make up to the volume with water, mix, filter immediately through a dry filter into a dry receiver and immediately determine the cyanamide nitrogen.

In both cases, determine the various soluble forms of nitrogen the same day the solution is made up, starting with cyanamide nitrogen and urea nitrogen, if they are present.

7.2.2 Total soluble nitrogen

7.2.2.1In the absence of nitrate

Transfer by pipette into a 300 ml Kjeldahl flask, an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2), containing not more than 100 mg of nitrogen. Add 15 ml of concentrated sulfuric acid (4.12), 0.4 g of copper oxide or 1.25 g of copper sulfate (4.27) and a few anti-bump granules (4.28). First heat gently to begin the digestion and then at a higher temperature until the liquid becomes colourless or slightly greenish and white fumes are clearly apparent. After cooling, quantitatively transfer the solution into the distillation flask, dilute to about 500 ml with water and add a few anti-bump granules (4.28). Connect the flask to the distillation apparatus (5.1) and continue the distillation as described in paragraph 7.1.1.2.

7.2.2.2In the presence of nitrate

Transfer by pipette into a 500 ml Erlenmeyer flask, an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2) containing not more than 40 mg of nitric nitrogen. At this stage of the analysis the total quantity of nitrogen is not important. Add 100 ml of 30% sulfuric acid (4.15), 5 g of reduced iron (4.2) and immediately cover the Erlenmeyer flask with a watch glass. Heat gently until the reaction is steady but not vigorous. At this juncture stop the heating and allow the flask to stand for at least three hours at ambient temperature. With water, quantitatively transfer the liquid into a 250 ml graduated flask, leaving behind the undissolved iron and make up to the mark with water. Mix thoroughly, and transfer by pipette into a 300 ml Kjeldahl flask, an aliquot part containing not more than 100 mg of nitrogen. Add 15 ml of concentrated sulfuric acid (4.12), 0.4 g of copper oxide or 1.25 g of copper sulfate (4.27) and some anti-bump granules (4.28). First heat gently to begin the digestion and then at a higher temperature until the liquid becomes colourless or slightly greenish and white fumes are clearly apparent. After cooling transfer the solution quantitatively into the distillation flask, dilute to approximately 500 ml with water and add some anti-bump granules (4.28). Connect the flask to the distillation apparatus (5.1) and continue the determination as described in paragraph 7.1.1.2.

7.2.2.3Blank test

See 7.1.1.3.

7.2.2.4Expression of result

No math image to display

where:

a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the blank.

A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for analysis.

M = mass of the sample, expressed in grams, present in the aliquot part taken for analysis.

7.2.3 Total soluble nitrogen with the exception of nitric nitrogen

Transfer by pipette into a 300 ml Kjeldahl flask, an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2) containing not more than 50 mg of nitrogen. Dilute to 100 ml with water, add 5 g of ferrous sulfate (4.16), 20 ml of concentrated sulfuric acid (4.1) and some anti-bump granules (4.28). First heat gently and then increase the heat until white fumes appear. Continue the digestion for 15 minutes. Stop the heating, introduce the copper oxide (4.27) as a catalyst and keep it at a temperature such that white fumes are emitted for a further 10 to 15 minutes. After cooling, quantitatively transfer the contents of the Kjeldahl flask into the distillation flask of the apparatus (5.1). Dilute to approximately 500 ml with water and add a few anti-bump granules (4.28). Connect the flask to the distillation apparatus and continue the determination as described in paragraph 7.1.1.2.

7.2.3.1Blank test

See 7.1.1.3

7.2.3.2Expression of result

No math image to display

where:

a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the blank.

A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for analysis.

M = mass of the sample, expressed in grams, present in the aliquot part taken for analysis.

7.2.4 Nitric nitrogen is obtained:

7.2.4.1In the absence of calcium cyanamide

By the difference between the results obtained in paragraphs 7.2.2.4 and 7.2.3.2 and/or the result obtained in paragraph 7.2.2.4 and the sum of the results obtained in paragraphs 7.2.5.2 or 7.2.5.5 and 7.2.6.3 or 7.2.6.5 or 7.2.6.6.

7.2.4.2In the presence of calcium cyanamide

By the difference between the results obtained in paragraphs 7.2.2.4 and 7.2.3.2 and between the result obtained in paragraph 7.2.2.4 and the sum of the results obtained in paragraphs 7.2.5.5 and 7.2.6.3 or 7.2.6.5 or 7.2.6.6 and 7.2.7.

7.2.5 Ammoniacal nitrogen

7.2.5.1Solely in the presence of ammoniacal nitrogen and ammoniacal + nitric nitrogen

Transfer by pipette into the flask of the distillation apparatus (5.1) an aliquot portion of the filtrate (7.2.1.1) containing not more than 100 mg of ammoniacal nitrogen. Add water to obtain a total volume of about 350 ml and some anti-bump granules (4.28) to facilitate boiling. Connect the flask to the distillation apparatus, add 20 ml of sodium hydroxide solution (4.9) and distil as described in paragraph 7.1.1.2.

7.2.5.2Expression of result

No math image to display

where:

a = ml of standard solution or potassium hydroxide (0.2 M) used for the blank.

A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the analysis.

M = mass of the sample, expressed in grams, present in the aliquot part taken for analysis.

7.2.5.3In the presence of urea and/or cyanamide nitrogen

Transfer by pipette into the dry flask of the apparatus (5.2), an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2) containing not more than 20 mg of ammoniacal nitrogen. Then assemble the apparatus. Transfer by pipette into the 300 ml Erlenmeyer flask 50 ml of the standard sulfuric acid solution 0.1 M (4.17) and enough distilled water for the level of the liquid to be approximately 5 cm above the opening of the delivery tube; add the indicator (4.29.1). Introduce, through the side neck of the reaction flask, distilled water to make up the volume to about 50 ml and mix. To avoid foaming during aeration, add a few drops of octan-1-ol (4.18). Make the solution alkaline by adding 50 ml of saturated potassium carbonate solution (4.19) and immediately begin to expel the ammonia thus liberated from the cold suspension. A strong current of air is necessary (flow of approximately 3 litres per minute) and should be purified beforehand by passing it through washing flasks containing dilute sulfuric acid and dilute sodium hydroxide. Instead of using pressurised air, it is also possible to use a vacuum (water pump) provided that the inflow tube is connected in a sufficiently airtight manner to the receiver used to collect the ammonia. The liberation of the ammonia is generally complete after three hours. It is nevertheless advisable to verify this by changing the receiving flask. When the operation is finished, disconnect the flask from the apparatus, rinse the tip of the tube and the sides of the flask with a little distilled water. Titrate the excess acid with standard sodium hydroxide solution (0.1 M) (4.20) to the end point of the indicator (4.29.1).

7.2.5.4Blank test

See 7.1.1.3.

7.2.5.5Expression of result

No math image to display

where:

a = ml of standard solution of sodium or potassium hydroxide (0.1 M) used for the blank.

A = ml of standard solution of sodium or potassium hydroxide (0.1 M) used for the analysis.

M = mass of the sample, expressed in grams, present in the aliquot part taken for analysis.

7.2.6 Ureic nitrogen

7.2.6.1Urease method

Transfer by pipette into a 500 ml graduated flask, an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2) containing not more than 250 mg of ureic nitrogen. To remove phosphates add saturated barium hydroxide solution (4.21) until no further precipitation occurs. Eliminate the excess of barium ions and any dissolved calcium ions by adding 10% sodium carbonate solution (4.22). Allow the precipitate to settle and check whether total precipitation has occurred. Make up to the mark, mix and filter through a pleated filter. Transfer by pipette 50 ml of the filtrate into the 300 ml Erlenmeyer flask of the apparatus (5.3). Acidify the filtrate with 2 M hydrochloric acid (4.23), until a pH of 3.0 measured by the pH meter (5.5) is obtained. Then raise the pH to 5.4 with 0.1 M sodium hydroxide solution (4.20).

To avoid losses of ammonia during reaction with urease, close the Erlenmeyer flask with a stopper provided with a separating funnel and a small bubble trap containing exactly 2 ml of standard 0.1 M hydrochloric acid (4.24). Introduce through the separating funnel 20 ml of urease solution (4.25), and allow to stand for one hour at 20 – 25 C. Transfer by pipette 25 ml of standard 0.1 M hydrochloric acid (4.24) into the separating funnel, allow it to run through into the solution and then rinse with a little water. In the same way transfer quantitatively the contents of the bubble trap into the solution contained in the Erlenmeyer flask. Titrate the excess acid with the standard solution of sodium hydroxide (0.1 M) (4.20), until a pH of 5.4 is obtained, measured by the pH meter.

7.2.6.2Blank test

See 7.1.1.3.

7.2.6.3Expression of result

No math image to display

where:

a = ml of standard solution of sodium or potassium hydroxide (0.1 M) used for the blank, carried out exactly under the same conditions as the analysis.

A = ml of standard solution of sodium or potassium hydroxide (0.1 M) used for the analysis.

M = mass of the sample, expressed in grams, present in the aliquot part taken for analysis.

Remarks

(1)
After precipitation by the solutions of barium hydroxide and sodium carbonate, make up to the mark, filter and neutralise as rapidly as possible.

(2)
The titration may also be carried out with the indicator (4.29.2), but the end point is then more difficult to observe.

7.2.6.4Gravimetric method with xanthydrol

Transfer by pipette into a 250 ml beaker, an aliquot portion of the filtrate (7.2.1.1 or 7.2.1.2) containing not more than 20 mg of urea. Add 40 ml of acetic acid (4.14). Stir with a glass rod for one minute, allow any precipitate to settle for five minutes. Filter into a 100 ml beaker, wash with several ml of acetic acid (4.14), then add to the filtrate drop by drop, 10 ml of xanthydrol solution (4.16), stirring continuously with a glass rod. Allow to stand until the precipitate appears, then stir again for one or two minutes. Allow to stand for one and half hours. Filter through a sintered glass crucible (5.7) which has been previously dried and weighed, using a slight reduction in pressure. Wash three times with 5 ml ethanol (4.31) without trying to remove all the acetic acid. Place it in the oven (5.6) at a temperature of 130 C for one hour (do not exceed 145 C). Allow to cool in a desiccator and weigh.

7.2.6.5Expression of result

No math image to display

where:

m = mass of the precipitate obtained, in grams.

M = mass of the sample, in grams, present in the aliquot part taken for analysis. Correct for the blank.

Note:although biuret will also be precipitated by xanthydrol, this should not give rise to a significant error in the determination since its level is generally low.

7.2.6.6Method of difference

Ureic nitrogen may also be calculated according to the following table: —

Case
Nitric Nitrogen
Ammoniacal Nitrogen
Cyanamide Nitrogen
Ureic Nitrogen

1
Absent
Present
Present
(7.2.2.4) – (7.2.5.5+7.2.7)

2
Present
Present
Present
(7.2.3.2) – (7.2.5.5+7.2.7)

3
Absent
Present
Absent
(7.2.2.4) – (7.2.5.5)

4
Present
Present
Absent
(7.2.3.2) – (7.2.5.5)

7.2.7 Cyanamide Nitrogen

Take an aliquot part of the filtrate (7.2.1.2), containing 10 to 30 mg of cyanamide nitrogen and place it in a 250 ml beaker. Continue the analysis according to Method 6.

8.    VERIFICATION OF RESULTS

In certain cases, a difference may be found between the total nitrogen obtained directly from a weighed out sample (paragraph 7.1) and total soluble nitrogen (paragraph 7.2.2). Nevertheless, the difference should not be greater than 0.5%. If this is not the case, the fertiliser contains forms of insoluble nitrogen not specified for fertilisers covered by the list in paragraph 2.

Before each analysis, check that the apparatus is working properly and that the correct application of the method is used, with a standard solution including the various forms of nitrogen in proportions similar to those of the test sample. This standard solution is prepared from solutions of potassium thiocyanate (4.3), potassium nitrate (4.4), ammonium sulfate (4.5) and urea (4.6).

8b.DETERMINATION OF DIFFERENT FORMS OF NITROGEN IN THE SAME SAMPLE — IN THE ABSENCE OF CYANAMIDE NITROGEN

SCOPE

1.  This method is for the determination of any one form of nitrogen in the presence of any other form, but in the absence of cyanamide nitrogen.

FIELD OF APPLICATION

2.  This method is applicable to all fertilisers in Group 1(a) of Section A and Groups 1, 2 and 3 of Section B of the Table in Schedule 1 of the Fertilisers Regulations 1991 which contain exclusively nitric, ammoniacal or ureic nitrogen.

PRINCIPLE

3.  The following determinations are made on different portions of a single sample solution.

Total soluble nitrogen

3.1—3.1.1 In the absence of nitrates, by direct Kjeldahl digestion of the solution.

3.1.2 In the presence of nitrates, by Kjeldahl digestion of a portion of the solution after reduction by the Ulsch method; ammonia is determined in both cases as described in Method 2.

3.2  Total soluble nitrogen except nitric nitrogen, by Kjeldahl digestion after elimination of nitric nitrogen in acid medium by means of ferrous sulfate; ammonia is determined as described in Method 2.

3.3  Nitric nitrogen, by difference: between 3.1.2 and 3.2 and/or between total soluble nitrogen (3.1.2) and the sum of ammoniacal and ureic nitrogen (3.4+3.5).

3.4  Ammoniacal nitrogen, by cold distillation of a weak alkaline solution; the ammonia is absorbed in a solution of sulfuric acid and determined as described in Method 2.

3.5  Ureic nitrogen, either:

3.5.1 By conversion using urease, into ammonia, which is determined by titration with a standard solution of hydrochloric acid;

or,

3.5.2 By gravimetry using xanthydrol: although biuret will also be precipitated by xanthydrol, this should not give rise to a significant error in the determination since its level is generally low in absolute value in compound fertilisers,

or,

3.5.3 By difference, according to the following table:

Case
Nitric nitrogen
Ammoniacal nitrogen
Difference

1
Absent
Present
(3.1.1) – (3.4)

2
Present
Present
(3.2) – (3.4)

4.    REAGENTS

Potassium sulfate.

Iron powder, reduced with hydrogen (the prescribed quantity of iron must be able to reduce at least 50 mg nitric nitrogen).

Potassium nitrate.

Ammonium sulfate.

Urea.

Sulfuric acid, 0.1 M solution.

Sodium hydroxide solution 30 g per 100 ml, ammonia free.

Sodium or potassium hydroxide, 0.2 M solution, free of carbonates.

Sulfuric acid (p=1.84 g/ml).

Hydrochloric acid solution: dilute an appropriate volume of hydrochloric acid (p=1.18 g/ml) with an equal volume of water.

Glacial acetic acid.

Sulfuric acid solution, approximately 30% (W/V) H2SO4.

Ferrous sulfate, crystalline FeSO4.7H2O.

Sulfuric acid, 0.05 M solution.

Octan-1-ol.

Potassium carbonate, saturated solution.

Sodium or potassium hydroxide, 0.1 M solution.

Barium hydroxide, saturated solution.

Sodium carbonate solution, 10 g per 100 ml.

Hydrochloric acid, 2 M solution.

Hydrochloric acid, 0.1 M solution.

Urease solution: suspend 0.5 g active urease in 100 ml distilled water. Using 0.1 M hydrochloric acid (4.21), adjust to pH 5.4, measured with pH meter.

Xanthydrol solution, 5 g per 100 ml in ethanol or methanol (4.28) (do not use products giving a high proportion of insoluble material). The solution can be kept for 3 months in a carefully stoppered bottle in the dark.

Catalyst: copper oxide (CuO), 0.3 to 0.4 g per determination, or an equivalent amount of copper sulfate pentahydrate, (0.95 to 1.25 g).

Anti-bump granules of pumice stone washed with hydrochloric acid and ignited.

Indicator solutions:

4.26.1 Mixed indicator: Solution A: dissolve 1 g methyl red in 37 ml 0.1 M sodium hydroxide solution and make up to 1 litre with water. Solution B: dissolve 1 g methylene blue in water and make up to 1 litre. Mix 1 volume of solution A and 2 volumes of solution B. This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution; use 0.5 ml (10 drops) of this indicator.

4.26.2 Methyl red indicator solution: Dissolve 0.1 g methyl red in 50 ml 95% ethanol, make up to 100 ml with water and filter if necessary; 4 – 5 drops of this indicator can be used instead of the previous one.

Indicator papers: litmus, bromothymol blue (or other papers sensitive in the range pH 6 – 8).

Ethanol or methanol, 95% (V/V).

5.    APPARATUS

Distillation apparatus. See Method 2.

Apparatus for determination of ammoniacal nitrogen. An example of the recommended apparatus is reproduced in Figure 6 in the Appendix.

Apparatus for determination of ureic nitrogen by the urease method (7.6.1). An example of the recommended apparatus is reproduced in Figure 7 in the Appendix.

Rotary shaker: 35 – 40 turns per minute.

pH meter.

Sintered glass crucibles, diameter of pores 5 to 15 microns.

6.    PREPARATION OF SAMPLE

See Method 1.

7.    PROCEDURE

Preparation of solution for analysis

7.1  Weigh to the nearest 0.001 g, 10 g of the prepared sample and transfer to a 500 ml graduated flask. Add 50 ml water and then 20 ml dilute hydrochloric acid (4.10) and mix. Allow to stand until the evolution of carbon dioxide ceases. Add 400 ml water, shake for half an hour; make up to volume with water, mix, filter through a dry filter into a dry container.

Total nitrogen

7.2—7.2.1 In the absence of nitrates

Transfer by pipette into a 300 ml Kjeldahl flask an aliquot portion of the filtrate (7.1) containing a maximum of 100 mg nitrogen. Add 15 ml concentrated sulfuric acid (4.9), 0.4 g copper oxide or 1.25 g copper sulfate (4.24) and a few glass beads to control boiling. Heat moderately at first in order to initiate the reaction, then more strongly until the liquid becomes colourless or slightly greenish and white fumes appear. After cooling, transfer the solution into the distillation flask, dilute to about 500 ml with water and add a few granules of pumice stone (4.25). Connect the flask to the distillation apparatus (5.1) and carry out the determination as described in Method 8a, 7.1.1.2.

7.2.2 In the presence of nitrates

Transfer by pipette into a 500 ml Erlenmeyer flask a aliquot portion of the filtrate (7.1) containing not more than 40 mg nitric nitrogen. At this stage of the analysis, the total quantity of nitrogen is unimportant. Add 10 ml of 30% sulfuric acid (4.12), 5 g reduced iron (4.2) and immediately cover the Erlenmeyer flask with a watch glass. Heat gently until the reaction becomes strong but not violent. Stop heating and allow to stand for at least 3 hours at ambient temperature. Transfer the liquid quantitatively to a 250 ml graduated flask, ignoring undissolved iron. Make up to the mark with water and mix carefully. Transfer by pipette a portion containing a maximum of 100 mg nitrogen into a 300 ml Kjeldahl flask. Add 15 ml concentrated sulfuric acid (4.9), 0.4 g copper oxide or 1.25 g copper sulfate (4.24) and a few glass beads.

Heat moderately at first in order to initiate the reaction, then more strongly until the liquid becomes colourless or slightly greenish and white fumes appear. After cooling, transfer the solution quantitatively to the distillation flask, dilute to about 500 ml with water and add a few granules of pumice stone (4.25). Connect the flask to the distillation apparatus (5.1) and continue the determination as described in Method 8a, 7.1.1.2.

7.2.3 Blank test

Carry out a blank test under the same conditions (omitting only the sample), and use this value in the calculation of the final result.

7.2.4 Expression of result

No math image to display

where:

a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the blank, carried out under the same conditions as the analysis.

A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the analysis.

M = mass of the sample, in grams, present in the aliquot part taken for analysis.

Total nitrogen excluding nitric nitrogen

7.3  7.3.1 Transfer by pipette into a 300 ml Kjeldahl flask an aliquot portion of the filtrate (7.1) containing not more than 50 mg of nitrogen. Dilute to 100 ml with water, add 5 g ferrous sulfate (4.13), 20 ml concentrated sulfuric acid (4.9) and a few glass beads to control boiling (425). Heat moderately at first then more strongly until white fumes appear. Continue the reaction for 15 minutes. Stop heating, introduce 0.4 g copper oxide or 1.25 g copper sulfate (4.24) as catalyst, resume heating and maintain production of white fumes for 10 – 15 minutes. After cooling, transfer the contents of the Kjeldahl flask quantitatively to the distillation flask (5.1). Dilute to about 500 ml with water and add a few granules of pumice stone (4.25). Connect the flask to the distillation apparatus and continue the determinations as in Method 8a, 7.1.1.2.

7.3.2 Blank test

See 7.2.3.

7.3.3 Expression of result

No math image to display

where:

a = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the blank.

A = ml of standard solution of sodium or potassium hydroxide (0.2 M) used for the analysis.

M = mass of the sample, in grams, present in the aliquot part taken for analysis.

Nitric nitrogen is obtained: by difference between

7.4  (7.2.4) – (7.5.3+7.6.3)

or (7.2.4) – (7.5.3+7.6.5)

or (7.2.4) – (7.5.3+7.6.6)

Ammoniacal nitrogen

7.5—7.5.1 In the presence of ureic nitrogen

Transfer by pipette into the dry flask of the apparatus (5.2) an aliquot portion of the filtrate (7.1) containing a maximum of 20 mg ammoniacal nitrogen. Connect up the apparatus. Place in the 300 ml Erlenmeyer flask 50.0 ml standard 0.05 M sulfuric acid solution (4.14) and an amount of distilled water such that the level of the liquid is about 5 cm above the opening of the intake tube. Introduce through the side neck of the reaction flask distilled water so as to bring the volume to about 50 ml and mix. To avoid foaming during aeration add several drops of octan-1-ol (4.15). Add 50 ml saturated potassium carbonate solution (4.16) and immediately begin to expel the ammonia thus released from the cold suspension. A strong current of air is necessary (flow rate of about 3 litres per minute) and should be purified beforehand by passing it through washing flasks containing dilute sulfuric acid and dilute sodium hydroxide. Instead of using air under pressure, a vacuum may be used (water pump) provided that the connections between the apparatus are air tight. The liberation of ammonia is generally complete after three hours. However, it is desirable to make certain of this by changing the Erlenmeyer flask. When the process is finished, disconnect the Erlenmeyer flask from the apparatus, rinse the end of the intake tube and the walls of the Erlenmeyer flask with a little distilled water and titrate the excess acid against standard 0.1 M sodium hydroxide solution (4.17).

7.5.2 Blank test

See 7.2.3.

7.5.3 Expression of result

No math image to display

where:

a = ml of standard solution of sodium or potassium hydroxide (0.1 M) (4.17) used for the blank.

A = ml of standard solution of sodium or potassium hydroxide (0.1 M) (4.17) used for the analysis.

M = mass of the sample, in grams, present in the aliquot part taken for analysis.

Ureic nitrogen

7.6—7.6.1 Urease method

Transfer by pipette into a 500 ml graduated flask, an aliquot portion of the filtrate (7.1) containing not more than 250 mg of ureic nitrogen. To remove phosphates, add a suitable quantity of saturated barium hydroxide solution (4.18) until further addition does not cause the production of more precipitate. Eliminate excess barium ions (and any dissolved calcium ions) with 10% sodium carbonate solution (4.19). Allow to settle and check whether precipitation is complete. Make up to the mark, mix and filter through a fluted filter paper. Transfer by pipette 50 ml of filtrate into the 300 ml Erlenmeyer flask of the apparatus (5.3). Acidify with 2 M hydrochloric acid (4.20) to pH 3.0, measured by means of the pH meter (5.5). Raise the pH to 5.4 by the addition of 0.1 M sodium hydroxide (4.17). To avoid ammonia losses when hydrolysis by urease occurs, close the Erlenmeyer flask by means of a stopper provided with a dropping funnel and a small bubble trap containing exactly 2 ml standard 0.1 M hydrochloric acid solution (4.21). Introduce through the separating funnel, 20 ml urease solution (4.22). Allow to stand for one hour at 20 – 25 C. Place 25.0 ml of the standard 0.1 M hydrochloric acid solution (4.20) in the dropping funnel, allow to run into the solution, then rinse with a little water. Transfer quantitatively the contents of the bubble trap to the solution contained in the Erlenmeyer flask. Titrate the excess acid using standard 0.1 M sodium hydroxide solution (4.17), until a pH of 5.4 is obtained, measured on the pH meter.

Remarks

1.
After precipitation by barium hydroxide and sodium carbonate solutions, make up to the mark, filter and neutralise as quickly as possible.

2.
The titration may also be carried out using an indicator (4.26), although the change of colour is more difficult to observe.

7.6.2 Blank test

See 7.2.3.

7.6.3 Expression of result

No math image to display

where:

a = ml of standard solution of sodium or potassium hydroxide (0.1 M) (4.17) used for the blank, carried out in exactly the same conditions as the analysis.

A = ml of standard solution of sodium or potassium hydroxide (0.1 M) (4.17) used for the analysis.

M = mass of the sample, in grams, present in the aliquot part taken for analysis.

7.6.4 Gravimetric method using xanthydrol

Transfer by pipette into a 100 ml beaker an aliquot portion of the filtrate (7.1) containing not more than 20 mg urea. Add 40 ml acetic acid (4.11). Stir with a glass rod for one minute. Allow any precipitate to settle for five minutes. Filter, wash with a few ml acetic acid (4.11). Add 10 ml xanthydrol solution (4.23) to the filtrate drop by drop, stirring continuously with a glass rod. Allow to stand until the precipitate appears, then stir again for one or two minutes. Allow to stand for one and a half hours. Filter, using a slight reduction in pressure, through a sintered glass crucible (5.6) which has been previously dried and weighed. Wash three times with 5 ml ethanol (4.28), without trying to remove all the acetic acid. Place in an oven at a temperature of 130°C for one hour (do not exceed 145 C). Allow to cool in a desiccator and weigh.

7.6.5 Expression of result

No math image to display

where:

m = mass of the precipitate in grams.

M = mass of the sample, in grams, present in the aliquot part taken for analysis.

Correct for the blank.

Note: Although biuret will also be precipitated by xanthydrol, this should not give rise to a significant error in the determination since its level is generally low in absolute value in compound fertilisers.

7.6.6 Difference method

Ureic N can also be calculated as indicated in the following table:

Case
Nitric N
Ammoniacal N
Ureic N

1
Absent
Present
(7.2.4) – (7.5.3)

2
Present
Present
(7.3.3) – (7.5.3)

8.    VERIFICATION OF RESULTS

Before each analysis, check the functioning of the apparatus and the correct application of the methods used with a standard solution containing the different forms of nitrogen in proportions similar to those in the sample. This standard solution is prepared from solutions of potassium nitrate (4.3), ammonium sulfate (4.4) and urea (4.5).

9a.EXTRACTION OF TOTAL PHOSPHORUS BY MINERAL ACIDS

1.    SCOPE

This method is for the determination of phosphorus soluble in mineral acids.

2.    FIELD OF APPLICATION

Subject to regulation 6(3), applicable only to the phosphatic fertilisers listed in Group 2(a) of Section A and Groups 1, 2 and 4 of Section B of the Table in Schedule 1 of the Fertilisers Regulations 1991, and to phosphatic fertilisers listed in Groups 1 (a), 1 (b) and 2 of Section C of that table which are not designated as “EEC fertiliser”.

3.    PRINCIPLE

Extraction of the phosphorus in the fertiliser with a mixture of nitric acid and sulfuric acid.

4.    REAGENTS

Sulfuric acid (p=1.84 g/ml).

Nitric acid (p=1.40 g/ml).

5.    APPARATUS

A Kjeldahl flask, with a capacity of at least 500 ml, or a 250 ml round-bottomed flask with a glass tube forming a reflux condenser.

6.    PREPARATION OF THE SAMPLE

See Method 1.

7.    PROCEDURE

Extraction

7.1  Weigh to the nearest 0.001g 2.5 g of the prepared sample and place it in a dry Kjeldahl flask. Add 15 ml water and swirl to suspend the substance. Add 20 ml nitric acid (4.2) and carefully add 30 ml sulfuric acid (4.1). When the initial violent reaction has ceased, slowly bring the contents of the flask to boiling and boil for 30 minutes. Allow to cool and then carefully add with mixing about 150 ml water and boil for 15 minutes.

Cool completely and transfer the liquid quantitatively to a 500 ml graduated flask. Make up to volume, mix and filter through a dry fluted filter, discarding the first portion of the filtrate.

Determination

7.2  Determine the phosphorus using Method 10 on an aliquot portion of the clear filtrate.

Note: If the sample contains cellulose matter, the following procedure is suggested to avoid excessive frothing during digestion:

Weigh to the nearest 0.001 g, 2.5 g of the prepared sample and place it in a dry Kjeldahl flask. Add 30 ml sulfuric acid (4.1) and carefully boil until most of the organic matter has been destroyed. Allow to cool, add 15 ml water and 20 ml nitric acid (4.2); bring to the boil and continue boiling for 30 minutes. Continue as described in 7.1 from “Allow to cool and then …”.

9b.EXTRACTION OF PHOSPHORUS BY 2% FORMIC ACID

1.    SCOPE

This method is for the determination of phosphorus soluble in 2% formic acid.

2.    FIELD OF APPLICATION

Applicable only to soft natural phosphate.

3.    PRINCIPLE

To differentiate between hard natural phosphates and soft natural phosphates, phosphorus soluble in formic acid is extracted under specified conditions.

4.    REAGENTS

Formic acid, 2% (20 g per litre): dilute 82 ml formic acid (concentration 98 – 100% p = 1.22 g/ml) to 5 litres with distilled water.

5.    APPARATUS

500 ml graduated flask with a wide neck (eg Stohmann).

Rotary shaker, 35 – 40 turns per minute.

6.    PREPARATION OF THE SAMPLE

See Method 1.

7.    PROCEDURE

Extraction

Weigh to the nearest 0.001 g, 5 g of the prepared sample and place it in a dry 500 ml graduated flask (5.1). While continuously rotating the flask by hand, add the formic acid (4.1) (at 20+1 C) until it is approximately 1 cm below the graduation mark. Then make up to the volume. Close the flask with a rubber stopper and shake for 30 minutes (5.2). Filter the solution through a dry fluted filter, into a dry receiver, discarding the first portion of the filtrate.

Determination

Determine the phosphorus using Method 10 on an aliquot portion of the clear filtrate.

9c.EXTRACTION OF PHOSPHORUS BY 2% CITRIC ACID

1.    SCOPE

This method is for the determination of phosphorus soluble in 2% citric acid.

2.    FIELD OF APPLICATION

Subject to regulation 6(3) only applicable to basic slag fertilisers in Group 2(a) of Section A and Groups 1, 2 and 4 of Section B of the Table in Schedule 1 of the Fertilisers Regulations 1991.

3.    PRINCIPLE

Extraction of the phosphorus in the fertiliser with a 2% citric acid solution under specified conditions.

4.    REAGENT

2% citric acid solution (20 g per litre), prepared from citric acid monohydrate.

Note: Verify the concentration of this citric acid solution by titrating 10 ml with a 0.1M sodium hydroxide standard solution using phenolphthalein as an indicator. If the concentration is correct, the titre should be 28.55 ml.

5.    APPARATUS

Rotary shaker: 35 – 40 turns per minute.

PREPARATION OF THE SAMPLE

6.  The analysis is carried out on the product as received, without grinding, after carefully mixing the original sample to ensure it is homogeneous. See Method 1.

7.    PROCEDURE

Extraction

7.1  Weigh to the nearest 0.001 g, 5 g of the mixed sample and place it in a dry flask with a sufficiently wide neck, with a capacity of 600 ml, to allow the liquid to be shaken thoroughly. Add 500 ml+1 ml of the citric acid solution (4.1) at 20+1 C. When adding the first portion of the reagent shake vigorously by hand to stop the formation of lumps and to prevent the sample sticking to the sides. Close the flask with a rubber stopper and shake it on the rotary shaker (5.1) for exactly 30 minutes at a temperature of 20+2 C.

Filter immediately through a dry fluted filter, into a dry glass receiver and discard the first 20 ml of the filtrate. Continue the filtration until a sufficient quantity of filtrate is obtained to carry out the phosphorus determination.

Determination

7.2  Determine the phosphorus using Method 10 on an aliquot portion of the clear filtrate.

9d.EXTRACTION OF PHOSPHORUS BY NEUTRAL AMMONIUM CITRATE

1.    SCOPE

This method is for the determination of phosphorus soluble in neutral ammonium citrate.

2.    FIELD OF APPLICATION

Applicable to all fertilisers in Group 2(a) of Section A and Groups 1, 2 and 4 of Section B and Group 2 of Section C of the Table in Schedule 1 of the Fertilisers Regulations 1991 for which the declaration of the solubility in neutral ammonium citrate is prescribed.

3.    PRINCIPLE

Extraction of phosphorus at a temperature of 65 C using a neutral ammonium citrate solution (pH=7.0) under specified conditions.

4.    REAGENTS

Neutral ammonium citrate solution (pH=7.0).

This solution must contain 185 g of citric acid monohydrate per litre and must have a specific gravity of 1.09 at 20°C and a pH of 7.0. The reagent is prepared as follows:

Dissolve 370 g citric acid monohydrate in about 1.5 litres of water and make an approximately neutral solution by adding 345 ml of ammonia solution (28 – 29% of NH3). If the NH3 concentration is lower than 28% add a correspondingly larger quantity of ammonia solution and dilute the citric acid in correspondingly smaller quantities of water.

Cool and make exactly neutral by adding the ammonia solution (28 – 29% of NH3) drop by drop, stirring continuously (with a mechanical stirrer) until a pH of exactly 7.0 at 20°C is obtained, keeping the electrodes of the pH meter (5.1) immersed in the solution.

At this point make up the volume to 2 litres and test the pH again. Keep the reagent in a closed container and check the pH at regular intervals.

5.    APPARATUS

pH meter.

Water bath which can be set thermostatically at 65°C, equipped with a mechanically operated shaking tray (see Figure 8 in the Appendix).

6.    PREPARATION OF THE SAMPLE

See Method 1.

7.    PROCEDURE

Extraction

7.1  Transfer 1(9) or 3(10) grams, as appropriate, of the fertiliser to be analysed into a 200 or 250 ml Erlenmeyer flask containing 100 ml of ammonium citrate solution previously heated at 65°C. Stopper the Erlenmeyer flask and shake in order to suspend the fertiliser without forming lumps. Remove the stopper for an instant in order to balance the pressure and close the Erlenmeyer flask again. Place the flask in the water-bath (5.2) set to maintain the contents of the flask at exactly 65°C. Shake mechanically for one hour so as to ensure complete suspension of the sample.(11) The level of suspension in the flask must stay constantly below that of the water in the bath. After exactly one hour remove the Erlenmeyer flask from the water-bath. Cool immediately under running water to ambient temperature and transfer the contents quantitatively from the Erlenmeyer flask into a graduated 500 ml flask with a jet of water. Make up the volume with water. Mix thoroughly and filter through a dry fluted filter (medium speed) into a dry container, discarding the first part of the filtrate (about 50 ml).

About 100 ml of clear filtrate should be collected.

Determination

7.2  Determine the phosphorus using Method 10 in an aliquot portion of the clear filtrate.

9e.EXTRACTION OF PHOSPHORUS BY ALKALINE AMMONIUM CITRATE (PETERMANN'S METHOD) AT 65°C

1.    SCOPE

This method is for the determination of phosphorus soluble in alkaline ammonium citrate.

2.    FIELD OF APPLICATION

Applicable only to precipitated dihydrated dicalcium phosphate (CaHPO4.2H2O).

3.    PRINCIPLE

Extraction of phosphorus at a temperature of 65°C with an alkaline solution of ammonium citrate (Petermann) under specified conditions.

4.    REAGENTS

Petermann’s solution

4.1  Characteristics:

Citric acid monohydrate, 173 g per litre.

Ammonia, 42 g per litre ammoniacal nitrogen.

pH, between 9.4 and 9.7.

Preparation from diammonium citrate:

Dissolve 941 g diammonium citrate in about 3,500 ml water in a 5 litre graduated flask. Stand the flask in a bath of running water, mix and cool. Add, in small amounts, 430 ml of ammonia solution (p=0.880 g/ml), from a freshly opened bottle (or an equivalent amount of diluted ammonia, for example if p=0.906 g/ml then 502 ml are required). Adjust the temperature to 20°C, make up to volume with water and mix.

Preparation from citric acid and ammonia:

Dissolve 865 g citric acid monohydrate in about 2,500 ml distilled water in a container of about 5 litres capacity. Place the container in an ice bath and add in small amounts, shaking continually, 966 ml of ammonia solution (p=0.880 g/ml), from a freshly opened bottle (or an equivalent amount of diluted ammonia, for example if p=0.906 g/ml, then, 1,114 ml are required) . Adjust the temperature to 20°C, transfer to a 5 litre graduated flask, make up to the mark with distilled water and mix.

Check the ammoniacal nitrogen content as follows:

Transfer 25 ml of the solution into a 250 ml graduated flask, make up to volume with distilled water and mix. Determine the ammoniacal nitrogen content on 25 ml of this solution using Method 2. If the solution is correct, 15 ml 0.25 M H2SO4 are required — Calculate the concentration of ammoniacal nitrogen in the reagent solution (1 ml 0.25 M H2SO4=0.007g nitrogen).

If the concentration of ammoniacal nitrogen is greater than 42 g/litre, ammonia can be expelled by a stream of inert gas or by moderate heating to bring back the pH to 9.7. Carry out a second determination.

If the concentration of ammoniacal nitrogen is less than 42 g/litre, calculate the volume of ammonia solution required to achieve this level (1 ml ammonia solution, p=0.880 g/ml contains approximately 0.22g ammoniacal nitrogen). For each ml of ammonia solution required add 0.173 g of citric acid.

Whenever corrections are made to this reagent solution, it is imperative that the final concentration of both the citric acid and ammoniacal nitrogen are as specified.

5.    APPARATUS

Water bath which can be maintained at a temperature of 65 +1 C.

500 ml graduated flask with a wide neck (eg Stohmann).

6.    PREPARATION OF SAMPLE

See Method 1.

7.    PROCEDURE

Extraction

Weigh to the nearest 0.001g, 1 g of the prepared sample and transfer to the 500 ml graduated flask (5.2). Add 200 ml alkaline ammonium citrate solution (4.1). Stopper the flask and shake vigorously by hand to avoid the formation of lumps and to prevent any adherence of the sample to the sides.

Place the flask in the water bath at 65 C and shake every 5 minutes during the first half an hour. After each shaking, raise the stopper to equilibrate the pressure. The level of water in the water bath should be above the level of solution in the flask. Allow the flask to remain in the water bath a further hour at 65 C and shake every ten minutes. Remove the flask, cool to a temperature of about 20 C, make up to volume of 500 ml with water. Mix and filter through a dry fluted filter paper, rejecting the first portion of filtrate.

Determination

Determine the phosphorus using Method 10 on an aliquot portion of the clear filtrate.

9f.EXTRACTION OF PHOSPHORUS BY ALKALINE AMMONIUM CITRATE (PETERMANN'S) METHOD AT AMBIENT TEMPERATURE

1.    SCOPE

This method is for the determination of phosphorus soluble in alkaline ammonium citrate.

2.    FIELD OF APPLICATION

Applicable only to disintegrated phosphates.

3.    PRINCIPLE

Extraction of phosphorus at a temperature of 20°C with an alkaline solution of ammonium citrate (Petermann’s solution) under specified conditions.

4.    REAGENT

See Method 9e.

5.    APPARATUS

250 ml graduated flask with a wide neck (eg Stohmann).

Rotary shaker, 35 – 40 turns per minute.

6.    PREPARATION OF THE SAMPLE

See Method 1.

7.    PROCEDURE

Extraction

7.1  Weigh to the nearest 0.001 g, 2.5 g of the prepared sample and transfer to a 250 ml graduated flask (5.1). Add a little of Petermann’s solution (4) at 20°C, shake very hard in order to stop the formation of lumps and to prevent any of the sample adhering to the side of the flask. Make up to the mark with Petermann’s solution and close the flask with a rubber stopper.

Shake for two hours on the rotary shaker (5.2). Filter immediately through a dry fluted filter into a dry container, discarding the first portion of the filtrate.

Determination

7.2  Determine the phosphorus using Method 10 on an aliquot portion of the clear filtrate.

9g.EXTRACTION OF PHOSPHORUS BY ALKALINE AMMONIUM CITRATE (JOULIE'S METHOD)

1.    SCOPE

This method is for the determination of phosphorus soluble in Joulie’s alkaline ammonium citrate.

2.    FIELD OF APPLICATION

Applicable to all the straight and compound phosphatic fertilisers, in which the phosphate occurs in an aluminocalcic form.

3.    PRINCIPLE

Extraction by shaking vigorously with an alkaline solution of ammonium citrate of defined specification (and where appropriate in the presence of oxine), at about 20°C.

4.    REAGENTS

Joulie’s alkaline solution of ammonium citrate:

This solution contains 400 g of citric acid monohydrate and 153 g of NH3 per litre. Its free ammonia content is approximately 55 g per litre. It is prepared by one of the methods described below:

4.1.1 In a 1 litre graduated flask, dissolve 400 g of citric acid monohydrate in approximately 600 ml ammonia solution (p=0.925 g/ml), containing 200 g NH3 per litre; this may be prepared by diluting 760 ml ammonia solution (p=0.880 g/ml) from a freshly opened bottle with water to 1 litre. The citric acid is added successively in quantities of 50 to 80 g maintaining the temperature below 50 C. Make up the volume to 1 litre with ammonia solution (p=0.925 g/ml).

4.1.2 In a litre graduated flask, dissolve 432 g of diammonium citrate in 300 ml of water. Add 440 ml of ammonia solution (p=0.925 g/ml) (see 4.1.1 above). Make up the volume to 1 litre with water.

Verification of the total ammonia content:

Transfer a 10 ml sample of the citrate solution to a 250 ml flask. Make up the volume with distilled water. Determine the ammoniacal nitrogen content on 25 ml of this solution using Method 2. In these conditions the reagent is considered to be correct when the volume of 0.25 M sulfuric acid required is between 17.7 and 18.0 ml (1 ml 0.25 M H2SO4=0.008516g NH3). If the titre is too low add 4.25 ml of ammonia (p=0.925 g/ml) per 0.1 ml below the 18 ml indicated above.

8-Hydroxyquinoline (oxine), powdered.

5.    APPARATUS

Rotary shaker, 35 – 40 turns per minute.

500 ml graduated flask with a wide neck (Stohmann).

6.    PREPARATION OF THE SAMPLE

See Method 1.

7.    PROCEDURE

Extraction

7.1  Weigh to the nearest 0.0005 g, 1 g of the prepared sample and place in a small glass or porcelain mortar. Add about ten drops of ammonium citrate solution (4.1) to moisten it and then break it up very carefully with a pestle. Add 20 ml ammonium citrate solution (4.1), mix to a paste and leave to settle for about 1 minute.

Decant the liquid into a 500 ml graduated flask (5.2). Add 20 ml ammonium citrate solution (4.1) to the residue, grind as above and decant the liquid into the graduated flask. Repeat the process four times, so that by the end of the fifth time all the product can be poured into the flask. The total quantity of ammonium citrate solution used for these processes must be approximately 100 ml.

Rinse the residue from the pestle and mortar into the graduated flask with 40 ml of distilled water.

Stopper the flask and shake for three hours on the rotary shaker (5.1).

Leave the flask standing for fifteen to sixteen hours and then shake it again under the same conditions for three hours. The temperature during the whole process should be kept at 20°+2°C.

Make up to volume with distilled water and mix. Filter through a dry filter, discard the first portion of the filtrate and collect the clear filtrate in a dry flask.

Determination

7.2  Determine the phosphorus using Method 10 on an aliquot portion of the clear filtrate.

NOTE

8.  The use of oxine makes it possible to apply this method to fertilisers containing magnesium. This is recommended when the ratio of magnesium to phosphorus pentoxide is higher than 0.03 (Mg/P205>0.03). If this is the case, add 3 g of oxine to the moistened sample for analysis. The use of oxine in the absence of magnesium is not, moreover, likely to interfere subsequently with the determination. In the known absence of magnesium, oxine may be omitted.

9h.EXTRACTION OF PHOSPHORUS BY WATER

1.    SCOPE

This method is for the determination of water-soluble phosphorus.

2.    FIELD OF APPLICATION

Applicable to all fertilisers where water-soluble phosphorus is to be determined.

3.    PRINCIPLE

Extraction in water by shaking under specified conditions.

4.    APPARATUS

500 ml graduated flask with a wide neck (eg Stohmann).

Rotary shaker, 35 – 40 turns per minute.

5.    PREPARATION OF THE SAMPLE

See Method 1.

6.    PROCEDURE

Extraction

6.1  Weigh to the nearest 0.001 g, 5 g of the prepared sample and place it in a 500 ml graduated flask (4.1). Add 450 ml of water, the temperature of which must be between 20°C and 25°C. Close the flask and shake on the rotary shaker (4.2) for 30 minutes. Then make up to the mark with water, mix thoroughly and filter through a dry fluted paper into a dry container.

Determination

6.2  Determine the phosphorus using Method 10, on an aliquot portion of the clear filtrate.

10.DETERMINATION OF EXTRACTED PHOSPHORUS (Gravimetric method using quinoline phosphomolybdate)

1.    SCOPE

This method is for the determination of phosphorus in extracts from fertilisers.

2.    FIELD OF APPLICATION

This method is applicable to all extracts of fertilisers(12) for the determination of the different forms of phosphorus.

3.    PRINCIPLE

After hydrolysis, phosphorus is precipitated in an acidic solution in the form of quinoline phosphomolybdate. The precipitate is collected, washed, dried at 250°C and weighed.

In the above conditions, compounds likely to be found in the solution (mineral and organic acids, ammonium ions, soluble silicates, etc…) will not interfere provided that a reagent based on sodium molybdate or ammonium molybdate is used in the precipitation.

4.    REAGENTS

Concentrated nitric acid (p = 1.40 g/ml).

Molybdate reagent:

4.2.1 Preparation of the reagent based on sodium molybdate:

Solution A: dissolve 70 g sodium molybdate dihydrate in 100 ml water

Solution B: dissolve 60 g citric acid monohydrate in 100 ml water and 85 ml concentrated nitric acid (4.1).

Solution C: stir solution A into solution B to obtain solution C.

Solution D: to 50 ml water add 25 ml concentrated nitric acid (4.1), add 5 ml freshly distilled quinoline. Add this solution to solution C, mix thoroughly and leave standing overnight in the dark. Make up to 500 ml with water, mix again and filter through a sintered glass funnel (5.3).

4.2.2 Preparation of the reagent based on ammonium molybdate:

Solution A: dissolve 100 g ammonium molybdate in 300 ml water, heating gently and stirring from time to time.

Solution B: dissolve 120 g citric acid monohydrate in 200 ml water and add 170 ml of concentrated nitric acid (4.1).

Solution C: add 10 ml freshly distilled quinoline to 70 ml of concentrated nitric acid (4.1).

Solution D: slowly pour, stirring well, solution A into solution B. After thoroughly mixing, add solution C to this mixture and make up to 1 litre with water. Leave standing for two days in a dark place and filter through a sintered glass funnel (5.3).

The reagents 4.2.1 and 4.2.2 can be used in the same way; both must be kept in the dark in stoppered polyethylene bottles.

5.    APPARATUS

Filter crucible with porosity of 5 to 20 microns.

Drying oven regulated at 250°C+10°C.

Sintered glass funnel with porosity of 5 to 20 microns.

6.    PROCEDURE

Treatment of the solution

6.1  Using a pipette take an aliquot portion of fertiliser extract (see the Table) containing about 0.01 g of P2O5 and transfer to a 500 ml Erlenmeyer flask. Add 15 ml concentrated nitric acid(13) (4.1) and dilute with water to about 100 ml.

Hydrolysis

6.2  Bring the contents of the Erlenmeyer flask to the boil slowly and keep at this temperature until hydrolysis is completed (this usually takes 1 hour). Care must be taken to avoid losses by splashing and excessive evaporation which would reduce the initial volume by more than half, by fitting a reflux condenser. After hydrolysis make up to the initial volume with distilled water.

Weighing the crucible

6.3  Dry the filter crucible (5.1) for at least 15 minutes in the drying oven (5.2). Cool the crucible in a desiccator and weigh.

Precipitation

6.4  Heat the acid solution in the Erlenmeyer flask until it begins to boil and then precipitate the quinoline phosphomolybdate by adding 40 ml of the precipitating reagent (4.2.1 or 4.2.2)(14) drop by drop, stirring continuously. Place the Erlenmeyer flask in a steam bath for 15 minutes, shaking from time to time. The solution can be filtered immediately or after it has cooled down.

Filtering and Washing

6.5  Filter the solution under vacuum by decantation. Wash the precipitate in the Erlenmeyer flask with 30 ml water. Decant and filter the solution. Repeat this process five times. Quantitatively transfer the rest of the precipitate into the crucible washing it with water. Wash four times with 20 ml water, allowing the liquid to drain from the crucible before each addition.

Drying and weighing

6.6  Wipe the outside of the crucible with a filter paper. Place the crucible in the drying oven (5.2) for approximately 15 minutes. Cool in a desiccator and weigh rapidly, repeat this process until a constant mass is attained.

Blank test

6.7  For each series of determinations, make a blank test under the same conditions (omitting only the sample) and allow for this in the calculation of the final result.

Control test

6.8  Carry out the determination using an aliquot portion of a potassium dihydrogen phosphate solution containing 0.01 g of P2O5.

EXPRESSION OF RESULTS

7.  If the samples for analysis and dilutions shown in the Table are used the following formulae apply:

% P2O5 in the fertiliser = (A-a) × f

% P in the fertiliser = (A-a) × f'

where:

A = weight in g of the quinoline phosphomolybdate

a = mass in g of the quinoline phosphomolybdate obtained in the blank test

f and f' = factors given in the last two columns of the Table.

With samples for analysis and dilutions which differ from those of the Table the following formulae apply:

No math image to display
No math image to display

where:

F = conversion factor, quinoline phosphomolybdate into P2O5 = 0.0321

F' = conversion factor, quinoline phosphomolybdate into P=0.0140.

D = dilution factor

M = mass of the sample analysed.

TABLE FOR METHOD 10

%P2O5 in the fertiliser
% in the fertiliser
Sample for analysis g
Dilution to ml
Sample ml
Dilution to ml
Sample to be precipitated ml
Quinoline phosphomolybdate conversion factor (f) in percentage P2O5

Quinoline phosphomolybdate conversion factor (f1) in percentage P

1 – 5
0.44 – 2.2
1
500


100
16.04
7.00

2.5
500


50
12.83
5.60

5
500


25
12.83
5.60

5 – 10
2.2 – 4.4
1
500


50
32.07
14.00

2.5
500


25
25.66
11.20

3
500


25
21.38
9.33

5
500


10
32.07
14.00

10 – 25
4.4 – 11.0
1
500


25
64.15
28.00

2.5
500


10
64.15
28.00

3
500


10
53.46
23.33

5
500
50
500
50
64.15
28.00

+ 25
+: 11
1
500


10
160.40
70.01

2.5
500
50
500
50
128.30
55.99

3
500
50
500
50
106.90
46.66

5
500
50
500
25
128.30
55.92

11.DETERMINATION OF WATER-SOLUBLE POTASSIUM

1.    SCOPE

This method is for the determination of water-soluble potassium.

2.    FIELD OF APPLICATION

All the potassium fertilisers listed in Group 3(a) of Section A and Groups 1, 3 and 4 of Section B and Group 2 of Section C of the Table in Schedule 1 of the Fertilisers Regulations 1991.

3.    PRINCIPLE

The potassium is extracted with water and after the removal of interfering substances, the potassium is precipitated in a slightly alkaline medium in the form of potassium tetraphenylborate (KTPB).

4.    REAGENTS

Formaldehyde, 25 – 35% solution, filter if necessary before use.

Potassium chloride.

Sodium hydroxide, 10 M solution. Care should be taken to ensure that the sodium hydroxide is free from potassium.

Indicator solution: dissolve 0.5 g phenolphthalein in 100 ml 90% ethanol.

EDTA solution: 4 g of the dihydrated disodium salt of ethylenediaminetetra-acetic acid (EDTA) per 100 ml. Store this reagent in a plastic container.

STPB solution: dissolve 32.5 g sodium tetraphenylborate in 480 ml of water, add 2 ml sodium hydroxide solution (4.3) and 20 ml of a magnesium chloride solution (100 g of MgCl2.6H2O per litre). Stir for fifteen minutes and filter through a fine, ashless filter paper. Store this reagent in a plastic container.

Wash liquid: dilute 20 ml of the STPB solution (4.6) to 1 litre with water.

Bromine water: saturated bromine solution in water.

5.    APPARATUS

Filter crucibles with a porosity of 5 to 20 microns.

Oven regulated at 120° + 10° C.

6.    PREPARATION OF THE SAMPLE

See Method 1.

In the case of potassium salts the sample must be ground finely enough to ensure that a representative sample is obtained for analysis. For these products, Method 1, paragraph 6(a) must be used.

7.    PROCEDURE

Extraction

7.1  Weigh to the nearest 0.001 g, 10 g of the prepared sample (5 g for potassium salts containing more than 50% of potassium oxide or 20 g for fertilisers containing less than 5% of potassium oxide) and place in a 600 ml beaker with approximately 400 ml of water. Bring to the boil and maintain heat for 30 minutes. Cool, transfer quantitatively into a 1 litre graduated flask, make up the volume, mix and filter into a dry receiver. Discard the first 50 ml of the filtrate.

Note:If the filtrate is dark in colour, transfer by pipette, an aliquot portion containing at the most 100 mg of K20 and place in a 100 ml beaker, add bromine water and bring to the boil to eliminate any surplus bromine. After cooling transfer quantitatively to a 100 ml graduated flask, make up to the volume, filter and determine the potassium in an aliquot portion of the filtrate.

Determination

7.2  Transfer by pipette an aliquot portion of the filtrate containing 25-50 mg of potassium (see Table on page 50) into a 250 ml beaker; make up to 50 ml with water.

To remove interferences, add 10 ml of the EDTA solution (4.5), several drops of the phenolphthalein solution (4.4) and stir in, drop by drop, sodium hydroxide solution (4.3) until a red colour persists. Finally add a few more drops of sodium hydroxide to ensure an excess (usually 1 ml of sodium hydroxide is sufficient to neutralise the sample and ensure an excess).

Boil gently for 15 minutes to eliminate most of the ammonia. Add water to make the volume up to 60 ml.

Bring the solution to the boil, remove the beaker from the heat and add 10 ml formaldehyde (4.1). Add several drops of phenolphthalein solution (4.4) and if necessary, more sodium hydroxide solution until a distinct red colour appears. Cover the beaker with a watch glass and place it on a steam bath for fifteen minutes.

Weighing the crucible

7.3  Dry the filter crucible (5.1) to constant weight in the oven at 120° C (5.2) (about 15 minutes). Allow the crucible to cool in a desiccator and weigh it.

Precipitation

7.4  Remove the beaker from the steam bath, stir in drop by drop 10 ml of the STPB solution (4.6). This addition should take about 2 minutes; allow to stand for a least 10 minutes before filtering.

Filtering and washing

7.5  Filter under vacuum into the weighed crucible, rinse the beaker with the wash liquid (4.7), wash the precipitate three times with the wash liquid (60 ml in all of the wash liquid) and twice with 5 to 10 ml of water.

Drying and weighing

7.6  Wipe the outside of the crucible with a filter paper and place in the oven (5.2) for one and half hours at a temperature of 120° C. Allow the crucible to cool in a desiccator to ambient temperature and weigh rapidly.

Blank test

7.7  Carry out a blank test under the same conditions (omitting only the sample) and allow for this in the calculation of the final result.

Control test

7.8  Carry out the determination on an aliquot portion of an aqueous solution of potassium chloride, containing at the most 40 mg of K2O.

8.    EXPRESSION OF RESULTS

Method of calculation and formulae

8.1  If the quantities and the dilutions shown in the Table are used, the following formulae apply:

% K2O in the fertiliser = (A – a) × f

or

% K in the fertiliser = (A – a) × f1

where:

A = mass in grams of the precipitate from the sample

a = mass in grams of the precipitate from the blank

f and f1 = factors — see Table.

With samples and dilutions which differ from those shown in the Table use the following formulae:

No math image to display
or

No math image to display

where:

F = conversion factor, KTPB into K2O = 0.1314

F1 = conversion factor, KTPB into K = 0.109

D = dilution factor

M = mass in grams of sample for analysis.

TABLE FOR METHOD 11

% of K2O in the fertiliser
% of K in the fertiliser
Sample for analysis (g)
Aliquot portion to be taken as a sample for precipitation (ml)
Conversion factor f % K2O g KTPB
Conversion factor f1 % K g KTPB

1 – 5
0.8 – 4.2
20
50
13.14
10.91

5 – 10
4.2 – 8.3
10
50
26.28
21.81

10 – 20
8.3 – 16.6
10
25
52.56
43.62

20 – 50
16.6 – 41.5
10
10
131.40
109.10

more than 50
more than 41.5
5
10
262.80
218.10

12.DETERMINATION OF CHLORIDES IN THE ABSENCE OF ORGANIC MATERIAL

1.    SCOPE

This method is for the determination of chloride, in the absence of organic material.

2.    FIELD OF APPLICATION

All fertilisers which are free from organic material, except ammonium nitrate fertilisers of a nitrogen content greater than 28% by weight.

3.    PRINCIPLE

The chlorides, dissolved in water, are precipitated in an acid medium by an excess of standard solution of silver nitrate. The excess is titrated with a solution of ammonium thiocyanate in the presence of ferric ammonium sulfate (Volhard’s method).

4.    REAGENTS

Nitrobenzene or diethyl ether.

Nitric acid, 10 M solution.

Indicator solution: dissolve 40 g of ferric ammonium sulfate [Fe2(SO4)3.(NH4)2SO4.24H2O] in water and make up to 1 litre.

Silver nitrate, 0.1 M solution.

Ammonium thiocyanate, 0.1 M solution.

Preparation: since this salt is hygroscopic and cannot be dried without risk of decomposition, it is advisable to weigh out approximately 9g, dissolve in water and make up the volume to one litre. Standardise by titration against 0.1 M silver nitrate solution.

Potassium Chloride solution: Dissolve 2.103g of potassium chloride, previously dried at 130°C for one hour, in water and make up to 500ml.

5.    APPARATUS

Rotary shaker, 35 – 40 turns per minute.

PREPARATION OF SAMPLE

6.  See Method 1.

7.    PROCEDURE

Extraction

7.1  Weigh to the nearest 0.001 g, 5 g of the prepared sample and place in a 500 ml graduated flask and add 450 ml water. Shake for half an hour on the rotary shaker (5.1); make up to 500 ml with distilled water, mix and filter into a beaker, discarding the first part of the filtrate.

Determination

7.2  Take an aliquot portion of the filtrate containing not more than 0.150 g of chloride. If the portion taken is smaller than 50 ml it is necessary to make up the volume to 50 ml with distilled water. Add 5 ml 10 M nitric acid (4.2), 20 ml indicator solution (4.3), and two drops of ammonium thiocyanate standard solution (taken from a burette adjusted to zero). From a burette then add silver nitrate solution (4.4) until there is an excess of 2 to 5 ml. Add 5 ml nitrobenzene or 5 ml diethyl ether (4.1) and shake well to agglomerate the precipitate. Titrate the excess silver nitrate with 0.1 M ammonium thiocyanate (4.5) until a red-brown colour just appears which remains after the flask has been shaken slightly.

Note:Nitrobenzene or diethyl ether (especially the former) prevents the silver chloride from reacting with thiocyanate ions, thus a clear colour change is obtained.

Blank test

7.3  Carry out a blank test under the same conditions (omitting only the sample) and allow for this in the calculation of the final result.

Control test

7.4  Carry out the determination using 50ml (equivalent to 0.100g of chloride) of the potassium chloride solution (4.6).

EXPRESSION OF RESULT

8.  Express the result of the analysis as a percentage of chloride contained in the sample as it has been received for analysis.

Calculation: calculate the percentage of chloride (Cl) with the formula:

No math image to display

where:

Vz = number of millilitres of silver nitrate added

Vcz = number of millilitres of silver nitrate used in the blank test

Va = number of millilitres of ammonium thiocyanate used for the titration of the sample

Vca = number of millilitres of ammonium thiocyanate used for the titration of the blank

M = mass in grams of the sample in aliquot volume taken for titration.

13a.DETERMINATION OF FINENESS OF GRINDING — DRY METHOD

1.    SCOPE

This method is for the determination of the fineness of grinding by the dry method.

2.    FIELD OF APPLICATION

All fertilisers in Schedule 1 of the Fertilisers Regulations 1991 for which requirements are given of fineness of grinding using 0.630 mm and 0.160 mm sieves.

3.    PRINCIPLE

By mechanical sieve shaking, the quantities of product with a granule size greater than 0.63 mm and those with a granule size between 0.16 mm and 0.63 mm are determined and the percentage of fineness of grinding is calculated.

4.    APPARATUS

Mechanical sieve shaker.

Sieves with apertures of 0.160 mm and 0.630 mm respectively of standard ranges (diameter 20 cm, height 5 cm).

PROCEDURE

5.  Weigh to the nearest 0.05 g, 50 g of the sample. Assemble the two sieves and the collecting container on the shaker (4.1), the sieve with the larger apertures being placed on top. Place the sample for analysis on the top. Sieve for ten minutes and remove the part collected on the bottom. Sieve again for one minute and check that the amount collected on the bottom during this time is not more than 250 mg. Repeat the process (for one minute each time) until the amount collected is less than 250 mg. Weigh the residual material on both sieves separately.

EXPRESSION OF RESULTS

6.  Percentage of material passing sieve of 0.630 mm apertures = (50-M1) × 2

Percentage of material passing sieve of 0.160 mm apertures = [50-(Ml+M2)] × 2

where:

Ml = mass in g of residue on the sieve with 0.630 mm apertures

M2 = mass in g of residue on the sieve with 0.160 mm apertures

The results are to be rounded up to the nearest unit.

13b.DETERMINATION OF FINENESS OF GRINDING OF SOFT NATURAL PHOSPHATES

1.    SCOPE

This method is for determining the fineness of grinding of soft natural phosphates.

2.    FIELD OF APPLICATION

Soft natural phosphates.

3.    PRINCIPLE

For samples of fine particle size, agglomeration may occur thus making dry sieving difficult. For this reason, wet sieving is normally used.

4.    REAGENTS Sodium hexametaphosphate solution, 1 g per 100 ml.

5.    APPARATUS

Sieves with apertures of 0.063 mm and 0.125 mm respectively of standard ranges (diameter 20 cm, height 5 cm) and collecting containers.

Glass funnel of 20 cm diameter mounted on a stand.

Laboratory oven.

6.    PROCEDURE

Wash both sides of the sieves with water and place the sieve with 0.125 mm apertures above the 0.063 mm sieve.

Weigh to the nearest 0.05 g, 50 g of the prepared sample and place on the top sieve. Sieve under a small jet of cold water (tap water can be used) until the water is practically clear when it passes through. Care should be taken to ensure that the flow of water is such that the lower sieve never fills with water. When the residue on the top sieve seems to remain more or less constant, remove this sieve, and place on a collecting container (5.1) for the time being.

Continue the wet sieving through the lower sieve for a few minutes, until the water passing through is nearly clear. Replace the 0.125 mm sieve over the 0.063 mm sieve. Transfer any deposit from the collecting container to the top sieve and begin sieving again under a small jet of water until this water becomes almost clear once more.

Transfer each of the residues quantitatively into a separate 250 ml beaker by means of the funnel. Suspend each residue by filling the beakers with water. Allow to stand for about 1 minute and then decant as much water as possible. Place the beakers in the oven (5.3) at 150° C for two hours. Allow them to cool to room temperature in a desiccator, detach the residues with a brush and weigh them.

7.    EXPRESSION OF RESULTS

Percentage of material passing sieve of 0.125 mm apertures = (50-Ml) × 2

Percentage of material passing sieve of 0.063 mm apertures = [50-(Ml+M2)] × 2

where:

M1 = mass in g of the residue on the 0.125 mm sieve

M2 = mass in g of the residue on the 0.063 mm sieve.

The results are to be rounded up to the nearest unit.

8.    REMARK

If the presence of lumps is observed after sieving, the analysis should be carried out again in the following way:

Slowly pour 50 g of the sample into a 1 litre flask containing 500 ml of the sodium hexametaphosphate solution, stirring continuously. Stopper the flask and shake vigorously by hand to break up the lumps. Transfer the whole suspension into the top sieve and wash the flask thoroughly. Continue the analysis as described under paragraph 6.

14.METHODS OF ANALYSIS AND TEST PROCEDURES FOR AMMONIUM NITRATE FERTILISERS CONTAINING MORE THAN 28% NITROGEN BY WEIGHT



14a.METHOD FOR THE APPLICATION OF THERMAL CYCLES

SCOPE

1.  This method defines the procedure for the application of thermal cycles before carrying out the oil retention test on straight ammonium nitrate fertilisers containing more than 28% nitrogen by weight.

FIELD OF APPLICATION

2.  This procedure is for thermal cycling prior to determining the oil retention value of the fertiliser.

PRINCIPLE AND DEFINITION

3.  Heat the sample in an Erlenmeyer flask by immersing the flask in a water bath at 50° C and maintain at this temperature for two hours (phase at 50° C). Then cool the flask in a water bath at 25° C and maintain at this temperature for two hours (phase at 25° C). The combination of the two phases, first at 50° C then at 25° C, forms one thermal cycle.

APPARATUS

4.  Normal laboratory apparatus, in particular

4.1  Water baths thermostated at 25 (+1) and 50 (+1)° C respectively.

4.2  Erlenmeyer flasks with an individual capacity of 150 ml.

PROCEDURE

5.  Place each test sample of 70(+5) grams into an Erlenmeyer flask which is then closed with a stopper. Place the flask in the 50° C water bath for 2 hours, then transfer to the 25° C bath for a further 2 hours. Transfer the flask back into 50° C water bath for a further 2 hours and then return to the 25° C bath.

Maintain the water in each bath at constant temperature, stir fairly rapidly and ensure that the water level is above the level of the sample in the flask. Protect the stopper from condensation by a rubber cap or aluminium foil.

After two thermal cycles, keep the sample at 20+3° C for the determination of the oil retention value.

14b.DETERMINATION OF THE OIL RETENTION VALUE

1.    SCOPE AND FIELD OF APPLICATION

This method defines the procedure for the determination of the oil retention value of straight ammonium nitrate fertilisers containing more than 28% nitrogen by weight.

The method is applicable to both prilled and granular fertilisers which do not contain oil-soluble materials.

2.    DEFINITION

Oil retention value of a fertiliser: the quantity of oil retained by the fertiliser determined under the operating conditions specified and expressed as a percentage by mass.

3.    PRINCIPLE

Total immersion of the test portion in gas oil for a specified period, followed by the draining away of surplus oil under specified conditions. Measurement of the increase in mass of the test portion.

4.    REAGENT

Gas oil

Viscosity max:
5 mPas at 40° C

Density:
0.8 to 0.85 g/ml at 20° C

Sulfur content:
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