Fertilizers and soil conditioners -- Determination of microamounts of inorganic anions in fertilizers by ion chromatography

ISO 20702:2017 specifies the ion chromatography method for the determination of microamounts of water soluble inorganic anions, such as fluoride (F−), chloride (Cl−), bromide (Br−), iodide (I−), nitrite (NO2−) and thiocyanate (SCN−), in fertilizers.

Engrais et amendements -- Détermination des microquantités d'anions inorganiques dans les fertilisants par chromatographie d'échange d'ions

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Status
Published
Publication Date
07-Dec-2017
Current Stage
6060 - International Standard published
Start Date
25-Oct-2017
Completion Date
08-Dec-2017
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INTERNATIONAL ISO
STANDARD 20702
First edition
2017-12
Fertilizers and soil conditioners —
Determination of microamounts of
inorganic anions in fertilizers by ion
chromatography
Engrais et amendements — Détermination des microquantités
d'anions inorganiques dans les fertilisants par chromatographie
d'échange d'ions
Reference number
ISO 20702:2017(E)
ISO 2017
---------------------- Page: 1 ----------------------
ISO 20702:2017(E)
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© ISO 2017, Published in Switzerland

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ii © ISO 2017 – All rights reserved
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ISO 20702:2017(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 1

5 Reagents ........................................................................................................................................................................................................................ 1

6 Apparatus and materials.............................................................................................................................................................................. 3

7 Test procedure ........................................................................................................................................................................................................ 4

7.1 General ........................................................................................................................................................................................................... 4

7.2 Preparation of test sample ............................................................................................................................................................ 4

7.3 Activation of the filter columns................................................................................................................................................. 4

7.4 Preparation of the test solution ................................................................................................................................................ 4

7.5 Ion chromatography condition A (Gradient chromatography condition) ........................................... 5

7.6 Ion chromatography condition B (Isocratic chromatography condition)............................................ 6

7.7 Determination of standard working solutions and sample test solutions .......................................... 6

8 Calculation and expression of results ............................................................................................................................................. 7

8.1 General ........................................................................................................................................................................................................... 7

8.2 Precision ....................................................................................................................................................................................................... 7

8.2.1 Ring test ................................................................................................................................................................................... 7

8.2.2 Repeatability, r .................................................................................................................................................................. 7

8.2.3 Reproducibility, R ........................................................................................................................................................... 7

9 Test report ................................................................................................................................................................................................................... 7

Annex A (informative) Ring test report — Report of international laboratories ring test ..........................9

Annex B (informative) Typical ion chromatogram for gradient chromatography conditions ..............46

Annex C (informative) Typical ion chromatogram for isocratic chromatography conditions ..............47

Annex D (informative) Additional statistical index of the test results ...........................................................................48

Bibliography .............................................................................................................................................................................................................................50

© ISO 2017 – All rights reserved iii
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ISO 20702:2017(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following

URL: www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 134, Fertilizers and soil conditioners.

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ISO 20702:2017(E)
Introduction

Microamounts of inorganic anions such as fluoride, chloride, bromide, iodide, nitrite and thiocyanate

are usually contained in fertilizers. Excessive amounts of such inorganic anions can not only impede

the growth of crops, but can also cause harmful effects on the arable land and the environment.

Current standards around the world mostly focus on a few specific anions. This method, which uses

ion chromatography, provides a high-throughput screening and rapid determination pathway targeting

microamounts of six anions as an alternative to traditional chemical analysis.
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INTERNATIONAL STANDARD ISO 20702:2017(E)
Fertilizers and soil conditioners — Determination of
microamounts of inorganic anions in fertilizers by ion
chromatography
1 Scope

This document specifies the ion chromatography method for the determination of microamounts of

− − − −

water soluble inorganic anions, such as fluoride (F ), chloride (Cl ), bromide (Br ), iodide (I ), nitrite

− −
(NO ) and thiocyanate (SCN ), in fertilizers.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 8157, Fertilizers and soil conditioners — Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 8157 apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
4 Principle

Water soluble inorganic anions are extracted by sonication, centrifugation and purification using a

C18 column and a Ba-ion column (where applicable). During pre-treatment, the anions are filtered by

a 0,22 μm aqueous filter. They are determined by ion chromatography. Anions are separated based

on their affinity for the exchange sites on the analytical column. The suppressor device reduces

the background conductivity of the eluent to a low level by replacing the cations with the hydrogen

ions, thereby converting the anions in the fertilizer sample to their corresponding acids with higher

conductivity. The separated anions (in their acid forms) are measured by an electrical-conductivity

detector. Anions are identified based on their retention times compared to known standards.

Quantitation is accomplished by measuring the peak height or area compared to a calibration curve

generated from known standards.
5 Reagents

WARNING — Acetone and methanol are flammable and toxic. Refer to the applicable safety data

sheet (SDS). The related operations shall be performed in the fume hood. This document does

not point out all possible safety problems; therefore, the user shall bear the responsibility to

take proper safety and health measures.

Analytical grade reagent (A.R.) chemicals shall be used in all tests, unless otherwise indicated.

The purity of water used throughout shall be understood to mean reagent water with electrical

resistivity ≥18,2 MΩ·cm. In the list below, G.R. refers to guarantee reagent.
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ISO 20702:2017(E)
5.1 Ultrapure water, HPLC grade water with electrical resistivity ≥18,2 MΩ·cm.
5.2 Potassium hydroxide (G.R.).
5.3 Sodium carbonate (G.R.).
5.4 Sodium bicarbonate (G.R.).
5.5 Acetone, HPLC grade.
5.6 Methanol, HPLC grade.
NOTE Methanol is be used for the activation of SPE-C18 column (6.8).

5.7 Potassium hydroxide eluent. Dissolve 5,611 g potassium hydroxide (0,1 mol, 5.2) in water (5.1).

Dilute this solution to 1 l with water (5.1) and mix thoroughly. The potassium hydroxide solution can also

be prepared by automated eluent generation system (OH- type). The potassium hydroxide eluent is used

for gradient chromatography conditions.

5.8 Carbonate eluent. Dissolve 0,530 g sodium carbonate (5,0 mmol) (5.3) and 0,168 g sodium

bicarbonate (2,0 mmol) (5.4) in water (5.1), and add 40 ml of acetone (5.5) to the aqueous solution.

Dilute to 1 l with water (5.1) and mix thoroughly by ultrasonic treatment for 10 min. The carbonate

eluent is used for isocratic chromatography conditions.
5.9 Stock solutions
5.9.1 Fluoride stock solution (1 000 mg/l).

Dissolve 2,210 0 g NaF (sodium fluoride, A.R., pre-treated at 105 °C for 2 h) into water (5.1). Transfer the

aqueous solution into a 1 000 ml volumetric flask, dilute it to 1 l with water (5.1) and mix thoroughly.

Keep the fluoride stock solution in a polyethylene bottle for storage.
5.9.2 Chloride stock solution (1 000 mg/l).

Dissolve 1,648 0 g NaCl (sodium chloride, A.R., pre-treated at 105 °C for 2 h) in water (5.1). Transfer the

aqueous solution into a 1 000 ml volumetric flask, dilute it to 1 l with water (5.1) and mix thoroughly.

5.9.3 Bromide stock solution (1 000 mg/l).

Dissolve 1,490 0 g KBr (potassium bromide, A.R., pre-treated at 105 °C for 2 h) in water (5.1). Transfer

the aqueous solution into a 1 000 ml volumetric flask, dilute it to 1 l with water (5.1) and mix thoroughly.

Keep the bromide stock solution in an amber glass bottle for storage.
5.9.4 Iodide stock solution (1 000 mg/l).

Dissolve 1,308 0 g KI (potassium iodide, A.R., pre-treated at 105°C for 2 h) in water (5.1). Transfer the

aqueous solution into a 1 000 ml volumetric flask, dilute it to 1 l with water (5.1) and mix thoroughly.

Keep the iodide stock solution in an amber glass bottle for storage.
5.9.5 Nitrite stock solution (1 000 mg/l).

Dissolve 1,489 0 g NaNO (sodium nitrite, A.R., pre-dried in a desiccator for approximately 24 h) in

water (5.1). Transfer the aqueous solution into a 1 000 ml volumetric flask, dilute it to 1 l with water

(5.1) and mix thoroughly.
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ISO 20702:2017(E)

Nitrite is easily oxidized, especially in the presence of moisture, thus only fresh reagents are to be used.

Place approximately 2 g of NaNO in a 100 ml beaker and dry to constant weight (approximately 24 h) in

a desiccator. Preservation by refrigeration at 4 °C is required for nitrite.
5.9.6 Thiocyanate stock solution (1 000 mg/l).

Dissolve 1,673 0 g KSCN (potassium thiocyanate, pre-treated at 105 °C for 2 h) into water (5.1). Transfer

the aqueous solution into a 1 000 ml volumetric flask, dilute to 1 l with water (5.1) and mix thoroughly.

5.10 Anion standard working solutions.
− − − − − −

Prepare anion standard working solutions (including F , Cl , Br , I , NO and SCN ) in volumetric flasks

according to the concentration ranges listed in Table 1. Alternatively, certificated standard solutions of

single or mixed anions may also be used for the preparation of anion working solutions.

The concentration ranges for standard working solutions may be adjusted according to the levels

expected in the samples.

Preservation by refrigeration at 4 °C is required for solutions containing nitrite.

Table 1 — Preparation of anion standard working solutions
− − − − − −
Working F Cl Br I NO SCN
solution
mg/l mg/l mg/l mg/l mg/l mg/l
Blank 0 0 0 0 0 0
Standard 1 0,2 0,2 0,2 0,2 0,2 0,2
Standard 2 0,5 0,5 0,5 0,5 0,5 0,5
Standard 3 1,0 1,0 1,0 1,0 1,0 1,0
Standard 4 5,0 5,0 5,0 5,0 5,0 5,0
Standard 5 20,0 20,0 20,0 20,0 20,0 20,0
6 Apparatus and materials
6.1 Ion chromatograph, with electrical-conductivity detector.
6.2 Ultrasonic cleaner.
6.3 Centrifuge, with a rotational speed of 4 000 r/min.

NOTE Relative centrifugal force can be calculated as 0,000 001 18 times the rotational radius (in mm) times

the square of the revolutions per minute (r/min).
6.4 High speed pulverizer.
6.5 Analytical balance, with a sensitivity of 0,1 mg.
6.6 Syringe-driven filter, with an aqueous filter membrane with 0,22 μm pores.
6.7 Ba-ion filter column, 1 ml.

NOTE The Ba-ion filter column (for example, a Ba-Polystyrene resin column) is used to eliminate excess

amounts of sulfate and phosphate from the sample which can serve as potential interference.

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ISO 20702:2017(E)
6.8 SPE-C18 column, 1 ml.

NOTE The SPE-C18 column is used to eliminate interfering amounts of organic compounds from the sample

which can serve as potential interference.
6.9 Ag/H filter column, 1 ml.

NOTE Since chloride and nitrite elute very closely together, they are potential interferences for each other.

The Ag/H filter column is used to eliminate excess amounts of chloride to more accurately measure nitrite.

7 Test procedure
7.1 General
Two replicate experiments shall be done for the determination.
7.2 Preparation of test sample

Prepare a test portion by reducing the fertilizer sample to 100 g. Grind the sample until it passes through

a sieve of aperture size 0,5 mm and mix until homogenous. Place in a clean and dry bottle with a lid.

7.3 Activation of the filter columns
7.3.1 Activation of the Ba-ion filter column

Flush the Ba-ion filter column with 10 ml water (5.1) before use, keeping the water outflow velocity less

than 3 ml/min. The column shall be kept in stand-by mode after activation.
7.3.2 Activation of the SPE-C18 column

First, flush the SPE-C18 column with 5 ml methanol, keeping the methanol outflow velocity less than

3 ml/min. Then, flush the column with 15 ml water (5.1), keeping the water outflow velocity less than

3 ml/min. Keep the column flat for 20 min while it activates. The column shall be kept in stand-by mode

after activation.
7.3.3 Activation of the Ag/H filter column

Flush the Ag/H filter column with 10 ml water (5.1) before use; keep the water outflow velocity less

than 3 ml/min. The column shall be kept on stand-by after activation.
7.4 Preparation of the test solution

Accurately weigh to 0,000 2 g an appropriate amount (1 g to 2 g) of the ground test portion into a

100 ml volumetric flask and add water (5.1) to near 100 ml mark.

Choose a sample weight that ensures the concentrations of ions of interest lie within the following

− − −

ranges: F (10 mg/kg to 2 000 mg/kg), Cl (10 mg/kg to 20 000 mg/kg), Br (20 mg/kg to 2 000 mg/kg),

− − −

I (20 mg/kg to 2 000 mg/kg), NO (10 mg/kg to 2 000 mg/kg), SCN (40 mg/kg to 2 000 mg/kg).

Dissolve using an ultrasonic bath for 30 min, and then allow the contents of the volumetric flask to

reach the room temperature.
Dilute to volume with water (5.1), and mix thoroughly by shaking.

Centrifuge a 10 ml portion of the solution at a rotational speed of 4 000 r/min for 5 min to 10 min.

Remove 5 ml of supernatant from the centrifuge tube and filter with syringe-driven filter (6.6).

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ISO 20702:2017(E)

Filter the solution with tandem filter columns of SPE-C18 column (activated), Ba-ion filter column

(activated) and Ag/H filter column (activated) respectively, keeping the solution outflow velocity less

than 3 ml/min.

Discard the first 3 ml of filtrate and keep the remaining 1 ml to 2 ml solution for testing.

NOTE The SPE-C18 column is used to eliminate organic compounds as interferences in the test solution. The

Ba-ion filter column is used to eliminate excess amounts of sulfate and phosphate in the test solution. The Ag/H

filter column is used to eliminate excess chloride to accurately measure nitrite. The use of these filter columns is

dependent upon the sample being tested.
7.5 Ion chromatography condition A (Gradient chromatography condition)

7.5.1 Chromatographic column: hydroxide selective, gradient elution compatible, high capacity anion

exchange column.
7.5.2 Column temperature: 30 °C.

7.5.3 Suppressor device: membrane-based self-regenerating anion suppressor device. An equivalent

suppressor device may be used provided that comparable method detection limits can also be achieved

and that adequate baseline stability is attained.

7.5.4 Detector: electrical-conductivity detector with cell temperature held at 35 °C.

7.5.5 Eluent: potassium hydroxide eluent (5.6); gradient elution schedule listed in Table 2.

Table 2 — Gradient elution schedule
Time OH concentration
min (mmol·l )
0,00 12
13,00 12
14,00 80
46,00 80
47,00 12
54,00 12
7.5.6 Eluent flow rate: 1,0 ml/min.

7.5.7 Injection volume: 25 μl. The injection volume can be adjusted according to the concentrations of

ions of interest in the test solution.

Use the same size of sample loop for all standards, samples, and fortified samples. If removal of the

background matrix is not around 100 %, increasing the sample loop size will increase the overall mass

loading to the guard and the analytical columns, potentially saturating a column’s exchange capacity

and shifting retention times for the unknowns.
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ISO 20702:2017(E)
7.6 Ion chromatography condition B (Isocratic chromatography condition)

7.6.1 Chromatographic column: carbonate selective, high capacity anion exchange column.

7.6.2 Column temperature: 40 °C.

7.6.3 Suppressor device: self-regenerating anion suppressor device. An equivalent suppressor device

may be used provided that comparable method detection limits can also be achieved and that adequate

baseline stability is attained.

7.6.4 Detector: electrical-conductivity detector with cell temperature held at 35 °C.

7.6.5 Eluent: carbonate eluent (5.7), isocratic elution.
7.6.6 Eluent flow rate: 0,7 ml/min.

7.6.7 Injection volume: 20 μl. The injection volume can be adjusted according to the concentrations of

ions of interest in the test solution.
7.7 Determination of standard working solutions and sample test solutions
7.7.1 Determination of standard working solutions
− − − − − −

Use F , Cl , Br , I , NO and SCN standard solutions (5.10) to prepare the mixed-anion standard

working solutions given in Table 1. Plot the standard curves using the concentration of inorganic anions,

corresponding to the peak heights/areas obtained in the test.

Filter the mixed-anion standard working solutions with syringe-driven filter and tandem filter columns

of SPE-C18 column (activated) and Ba-ion filter column (activated), if necessary.

It is recommended to run a minimum of two standard curves for each set of unknowns, preferably at

the beginning and end of each set of unknowns. Additional standard curves are recommended for large

(>20) sets of unknowns.
7.7.2 Determination of sample test solutions

Test a blank solution and the sample test solutions under the same conditions as the standards. Use

the retention times to identify the inorganic anions, and derive the concentrations of inorganic anions

in the test solutions from the standard curves. Typical ion chromatograms are shown in Annex B (for

gradient chromatography conditions) and Annex C (for isocratic chromatography conditions).

The blank solution is prepared in the same manner as the test solutions, except for adding any test

samples.

If the response value (peak height/area) of any anion in a test solution exceeds the linear calibration

range of a standard solution, appropriate dilutions should be prepared.

For the determination of anions in liquid fertilizer, the instrumental detection limit (IDL, D.3) should be

verified before the analysis of the sample. For the determination of anions in liquid fertilizer containing

NO , the proposed method (7.5 and 7.6) shall be carried on very carefully, and anions standard working

solutions (5.10) shall be injected to identify the retention time of Br .
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ISO 20702:2017(E)
8 Calculation and expression of results
8.1 General
− − − − −

The mass fraction of fluoride (F ), chloride (Cl ), bromide (Br ), iodide (I ), nitrite (NO ) and

thiocyanate (SCN ), w, in the unit of mg/kg, is calculated using Formula (1):
()ρρ−×Vf×
w= (1)
where
− − − − −

ρ is the mass concentration of fluoride (F ), chloride (Cl ), bromide (Br ), iodide (I ), nitrite (NO )

and thiocyanate (SCN ), expressed in milligrams per litre (mg/l)of the test solutions;

− − − − −

ρ is the mass concentration of fluoride (F ), chloride (Cl ), bromide (Br ), iodide (I ), nitrite (NO )

0 2

and thiocyanate (SCN ), expressed in milligrams per litre (mg/l) of the blank solution;

V is the volume of the test/blank solutions, expressed in millilitres (ml);
f is the dilution factor of the test solutions;
m is the mass of the test portion, expresses in grams (g).

The determination result is the arithmetic average of two parallel determination results, and shall be

rounded off to three significant figures.
8.2 Precision
8.2.1 Ring test
Details of ring test on the precision of the method are summarized in Annex A.
8.2.2 Repeatability, r
− − − − − −
Anions F Cl Br I NO SCN
Repeatability limit,
10,424 0,882 0,802
0,015 x + 9,685 0,011 x + 1,336 0,050 x + 2,310 0,339 x 0,140 x
r, mg/kg
8.2.3 Reproducibility, R
− − − − − −
Anions F Cl Br I NO SCN
Reproducibility
20,020
0,889
0,484 x 0,137 x + 16,564 0,056 x + 29,554 0,255 x + 11,595 0,168 x + 11,155
limit, R, mg/kg
9 Test report
The test report contains the following information, at a minimum:
a) all information necessary for the complete identification of the sample;
b) test method used with reference to this document, i.e. ISO 20702:2017;

c) test results obtained (signal-to-noise ratio plots per unknown, instrument detection limits and

percent recoveries are suggested to be presented, if necessary. An explanation of these statistical

indices is provided in Annex D);
d) date of sampling and sampling procedure (if known);
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ISO 20702:2017(E)
e) date of analysis completion;
f) whether or not the requirement of the repeatability limit is fulfilled;

g) all operating details not specified in this document, or regarded as optional, together with details of

any incidents occurred when performing the method, which might have influenced the test results.

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ISO 20702:2017(E)
Annex A
(informative)
Ring test report — Report of international laboratories ring test
A.1 Overview

The international laboratories ring test of this document has been accomplished during March 2017

to May 2017. Fifteen laboratories participated in the two parallel tests on four test samples. This

international ring test was conducted by Shanghai Research Institute of Chemical Industry, Co. Ltd. and

Shanghai Entry-Exit Inspection and Quarantine Bureau, P. R. China. The statistician analysis and final

report was prepared by Shanghai Research Institute of Chemical Industry, Co. Ltd.

The following are the 15 laboratories that participated in the two parallel tests on four samples:

— Central Institute for Supervising and Testing in Agriculture, National Reference Laboratory, Division

of NRL Brno, Czech Republic;
— CF Industries Technical Service Laboratory, USA;
— China National Supervision and Testing Centre of Fine Chemicals;
— Hunan Testing Institute of Product and Commodity Supervision, P. R. China;

— Institution of Supervision and Inspection Product Quality of Guizhou Province, P. R. China;

— Metrohm China Limited;
— Ningbo Entry-Exit Inspection and Quarantine Bureau, P. R. China;
— Office of Indiana State Chemist, USA;

— Product Quality Supervising and Inspecting Centre of Taizhou city, P. R. China;

— Shaanxi Entry-Exit Inspection and Quarantine Bureau, P. R. China;
— Shandong Institute for Product Quality Inspection, P. R. China;
— Shanghai Research Institute of Chemical Industry, Co. Ltd., P. R. China;
— Shanghai Entry-Exit Inspection and Quarantine Bureau, P. R. China;
— Thermo Fisher Scientific Inc.;
— Yunnan Chemical Product Quality Supervision & Inspection Station, P. R. China.

NOTE Participating laboratories are listed in alphabetic order, which has no relation to the sequences listed

in the tables below.

The test method described in this document was adopted for the determination of fluoride, chloride,

bromide, iodide, nitrite and thiocyanate contents in the fertilizer samples.

Four different types of fertilizer samples were used during the ring test, each with several mean

levels. The test samples were: sample A (ammonium phosphate), sample B (nitro-compound fertilizer),

sample C (complex fertilizer) and sample D (potassium sulfate). The six anion contents to be determined

and involved in the statistics in the four fertilizer samples generally lie in the range of 10 mg/kg to

1 700 mg/kg, and the standard working solutions in the standard were designed to cover the range of

0 mg/kg to 2 000 mg/kg.
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ISO 20702:2017(E)
The precision of the test results was evaluate
...

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