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Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1996

Type Ni-Statutory-Rule

Publication 1996-10-31

State In force

Jurisdiction Northern Ireland

Department Government Printer for Northern Ireland

Source legislation.gov.uk

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Reform history JSON API

Made: 31st October 1996

Coming into operation: 16th December 1996

The Department of Agriculture in exercise of the powers conferred on it by sections 66(1), 74A, 75(1), 76(1), 77, 78(2), (4) and (6), 79(1), (2) and (9), 84 and 86(1), (2), (3), (5), (6), (7) and (9) of the Agriculture Act 1970[^f00001] and of all other powers enabling it in that behalf, after consultation as required by section 84(1) of that Act with such persons or organisations as appear to it to represent the interests concerned, hereby makes the following Regulations:—

Title, commencement and interpretation

1

(1) These Regulations may be cited as the Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1996 and shall come into operation on 16th December 1996.

(2) In these Regulations, “the Act” means the Agriculture Act 1970.

(3) 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.

(4) The Interpretation Act (Northern Ireland) 1954[^f00002] shall apply to these Regulations as it applies to a Measure of the Northern Ireland Assembly.

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) 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) 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 sub-paragraph (a) nor (b) 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.

Application of the methods of analysis

5

(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 (Northern Ireland) 1992[^f00003] shall be determined by the appropriate methods of analysis prescribed in Part I of Schedule 2.

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

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

(b) the amount of phosphorus soluble in 2% formic 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 table in Schedule 1 to the Fertilisers Regulations (Northern Ireland) 1992, fineness shall be determined by the appropriate method prescribed in Part I of Schedule 2.

Form of certificate of analysis

6

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

7

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

8

The following Regulations are hereby revoked—

(a) the Fertilisers (Sampling and Analysis) Regulations (Northern Ireland) 1991[^f00004];

(b) the Fertilisers (Sampling and Analysis) (Amendment) Regulations (Northern Ireland) 1992[^f00005]; and

SCHEDULE 1 — Manner of taking, marking, sealing and fastening up of samples

Part I — Definitions

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 II — General 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 are present.

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 III — Quantitative 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 1 kg in weight, the number of containers shall be selected in accordance with Table 1 in Part VI;

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

(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;

(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))	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))	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 IV — Taking 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, 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) 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 1 kg, 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 31.8 mm 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) 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 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);

(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 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) 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 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.

Part V — Marking, 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 than 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;

(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 VI — Sampling tables

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
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
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

SCHEDULE 2 — Methods of analysis

Part I

General

1

When two or more methods are prescribed in this Part 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 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.

Methods of Analysis

5

(1) Preparation of the sample for analysis

(2) Determination of ammoniacal nitrogen

(a) Determination of nitrate and ammoniacal nitrogen — Ulsch method

(b) Determination of nitrate and ammoniacal nitrogen — Arnd method

(a) Determination of the total nitrogen in calcium cyanamide — in the absence of nitrate

(b) Determination of the 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

(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

(a) Extraction of total phosphorus — by mineral acids

(b) Extraction of phosphorus — by 2% formic 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 matter

(13)

(a) Determination of fineness of grinding — dry method

(13)

(b) Determination of fineness of grinding of soft natural phosphates

(14) Methods of analysis and test procedures for ammonium nitrate fertiliser containing more than 28% nitrogen by weight

(a) Method for the application of thermal cycles

(b) Determination of the oil retention value

(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

(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

(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.

PRINCIPLE

2

(2.1) 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 appreciable affected.

(2.2) 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.

APPARATUS

3

(3.1) Sample divider (optional).

(3.2) Sieves with apertures of 0.2 mm and 0.5 mm.

(3.3) 250 ml flasks, stoppered.

(3.4) 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 4.1 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.

Final 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 ground 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.

SPECIAL CASES

6

Fertilisers comprising a blend of several categories of crystals a 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.

Residue which is difficult to grind and does not contain fertilising substances b Weigh the residue and take account of its mass when calculating the final result.

Products which decompose on heating c 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).

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

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.

REAGENTS

4

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

(4.2) Sulfuric acid, 0.05 M solution } for variant (a) (see page 21)

(4.3) Sodium or potassium hydroxide, 0.1 M solution, carbonate free } for variant (a) (see page 21)

(4.4) Sulfuric acid, 0.1 M solution } for variant (b) (see page 21)

(4.5) Sodium or potassium hydroxide, 0.2 M solution, carbonate free } for variant (b) (see page 21)

(4.6) Sulfuric acid, 0.25 M solution } for variant (c) (see page 21)

(4.7) Sodium or potassium hydroxide, 0.5 M solution, carbonate free } for variant (c) (see page 21)

(4.8) Sodium hydroxide solution, 30 g per 100 ml, ammonia free

(4.9) Indicator solutions:

(4.9.1) Mixed indicator:

Solution A: dissolve 1 g methyl red in 37 ml sodium hydroxide 0.1 M 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 solution.

(4.9.2) Methyl red indicator solution:

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.

APPARATUS

5

(5.1) 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.

(5.2) Rotary shaker, 35 to 40 turns per minute.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

Solubility test 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 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 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 page 21. 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 = m illilitres 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.$

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
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
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.

REAGENTS

4

(4.1) Hydrochloric acid solution, 50% (V/V): dilute an appropriate volume of hydrochloric acid (ρ = 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:

Mixed indicator: 4.7.1 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).

Methyl red indicator solution: 4.7.2 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.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

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.

REAGENTS

4

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

(4.2) Sulfuric acid, 0.05 M solution } for variant (a) (see page 21)

(4.3) Sodium or potassium hydroxide, 0.1 M solution, carbonate free } for variant (a) (see page 21)

(4.4) Sulfuric acid, 0.1 M solution } for variant (b) (see page 21)

(4.5) Sodium or potassium hydroxide, 0.2 M solution, carbonate free } for variant (b) (see page 21)

(4.6) Sulfuric acid, 0.25 M solution } for variant (c) (see page 21)

(4.7) Sodium or potassium hydroxide, 0.5 M solution, carbonate free } for variant (c) (see page 21)

(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:

Mixed indicator: 4.11.1 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).

Methyl red indicator solution: 4.11.2 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.

Congo red indicator solution: 4.11.3 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.

PROCEDURE

7

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 at 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% Al, 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.

REAGENTS

4

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

(4.2) Sulfuric acid, 0.05 M solution. } for variant (a) (see page 21)

(4.3) Sodium or potassium hydroxide, 0.1 M solution, carbonate free. } for variant (a) (see page 21)

(4.4) Sulfuric acid, 0.1 M solution. } for variant (b) (see page 21)

(4.5) Sodium or potassium hydroxide, 0.2 M solution, carbonate free. } for variant (b) (see page 21)

(4.6) Sulfuric acid, 0.25 M solution. } for variant (c) (see page 21)

(4.7) Sodium or potassium hydroxide, 0.5 M solution, carbonate free. } for variant (c) (see page 21)

(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 0.1M 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 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 (4 to 5 drops) may be used instead of the preceding one.

(4.11) Ethanol, 95%.

(4.12) Sodium nitrate.

APPARATUS

5

(5.1) 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 SAMPLE

6

See Method 1.

PROCEDURE

7

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 of Method 2. 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 of Method 2 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, 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 of 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.

REAGENTS

4

(4.1) Sulfuric acid solution 50% (V/V): dilute an appropriate volume of sulfuric acid (ρ = 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 1.25 g) for each determination.

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

(4.5) Sulfuric acid, 0.05 M solution. } for variant (a) (see page 21)

(4.6) Sodium or potassium hydroxide, 0.1 M solution, carbonate free. } for variant (a) (see page 21)

(4.7) Sulfuric acid, 0.1 M solution. } for variant (b) (see page 21)

(4.8) Sodium or potassium hydroxide, 0.2 M solution, carbonate free. } for variant (b) (see page 21)

(4.9) Sulfuric acid, 0.25 M solution. } for variant (c) (see page 21)

(4.10) Sodium or potassium hydroxide, 0.5 M solution, carbonate free. } for variant (c) (see page 21)

(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 (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.

APPARATUS

5

(5.1) Distillation apparatus. See Method 2.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

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

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.

REAGENTS

4

(4.1) Sulfuric acid (ρ = 1.84 g/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 21)

(4.5) Sodium or potassium hydroxide, 0.1 M solution, carbonate free. } for variant (a) (see page 21)

(4.6) Sulfuric acid, 0.1 M solution. for variant (b) } for variant (b) (see page 21)

(4.7) Sodium or potassium hydroxide, 0.2 M solution, carbonate free. } for variant (b) (see page 21)

(4.8) Sulfuric acid, 0.25 M solution. } for variant (c) (see page 21)

(4.9) Sodium or potassium hydroxide, 0.5 M solution, carbonate free. } for variant (c) (see page 21)

(4.10) Indicator solutions:

Mixed indicator: 4.10.1 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.

Methyl red indicator: 4.10.2 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.

Solution of stannous chloride: 4.11 Dissolve 120 g of stannous chloride (SnCl₂.2H₂.O) in 400 ml concentrated hydrochloric acid (ρ = 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 (ρ = 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 SAMPLE

6

See Method 1.

PROCEDURE

7

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.

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 applied 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.

REAGENTS

4

(4.1) Sulfuric acid, concentrated (ρ = 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 21)

(4.4) Sodium or potassium hydroxide, 0.1 M solution, carbonate free. } for variant (a) (see page 21)

(4.5) Sulfuric acid, 0.1 M solution. } for variant (b) (see page 21)

(4.6) Sodium or potassium hydroxide, 0.2 M solution, carbonate free.} for variant (b) (see page 21)

(4.7) Sulfuric acid, 0.25 M solution. } for variant (c) (see page 21)

(4.8) Sodium or potassium hydroxide, 0.5 M solution, carbonate free. } for variant (c) (see page 21)

(4.9) Indicator solutions:

Mixed indicator: 4.9.1 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).

Methyl red indicator: 4.9.2 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.

APPARATUS

5

(5.1) Distillation apparatus. See Method 2.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

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.

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.

REAGENTS

4

(4.1) Glacial acetic acid.

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

(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 (ρ = 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:

Mixed indicator: 4.10.1 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).

Methyl red indicator: 4.10.2 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.

APPARATUS

5

(5.1) Distillation apparatus. See Method 2.

(5.2) 500 ml graduated flask (e.g. Stohmann).

(5.3) Rotary shaker, 35-40 turns per minute.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

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.

EXPRESSION OF RESULT

8

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

7. — DETERMINATION OF BIURET IN UREA

SCOPE

1

This method is for the determination of biuret in urea.

FIELD OF APPLICATION

2

The method is applied exclusively to urea.

PRINCIPLE

3

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.

REAGENTS

4

(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[^f00007] 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.

APPARATUS

5

(5.1) Spectrophotometer.

PREPARATION OF SAMPLE

6

See Method 1.

PROCEDURE

7

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 with 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 0.001 g, 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

8

$$%biuret=C×2.5V$ 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

SCOPE

1

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

FIELD OF APPLICATION

2

Any fertiliser in Group 1(a) of Section A, and Groups 1, 2 and 3 of Section B of the Table in Schedule 1 to the Fertilisers Regulations (Northern Ireland) 1992[^f00008] containing nitrogen in various forms.

PRINCIPLE

3

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. 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. 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: Total soluble nitrogen 3.2.1 3.2.1.1 In the absence of nitrates, by direct Kjeldahl digestion. 3.2.1.2 In 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. Nitric nitrogen by difference 3.2.3 3.2.3.1 In 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). 3.2.3.2 In 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). Ammoniacal nitrogen 3.2.4 3.2.4.1 Solely in the presence of ammoniacal nitrogen and ammoniacal + nitric nitrogen, by applying Method 2. 3.2.4.2 In 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. Ureic nitrogen 3.2.5 Either 3.2.5.1 By conversion using urease into ammonia which is titrated with a standard solution of hydrochloric acid. or: 3.2.5.2 By 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: 3.2.5.3 By difference, according to the following table: CaseNitric NitrogenAmmoniacal NitrogenCyanamide NitrogenDifference 1AbsentPresentPresent(3.2.1.1)-(3.2.4.2 + 3.2.6)2PresentPresentPresent(3.2.2)-(3.2.4.2 + 3.2.6)3AbsentPresentAbsent(3.2.1.1)-(3.2.4.2)4PresentPresentAbsent(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.

REAGENTS

4

(4.1) Potassium sulfate.

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

(4.3) Potassium thiocyanate.

(4.4) Potassium nitrate.

(4.5) Ammonium sulfate.

(4.6) Urea.

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

(4.8) Sulfuric acid, 0.1 M solution.

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

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

(4.11) Stannous chloride solution:

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