CEN/TC 260

Date: 2025-11

prEN 17758:2026

Secretariat: DIN

Fertilizers and liming materials — Determination of the chloride content by potentiometric titration

Düngemittel und Kalkdünger - Bestimmung des Chloridgehaltes mittels potentiometrischer Titration

Engrais et amendements minéraux basiques - Détermination de la teneur en chlorures par titrage potentiométrique

ICS:

Contents Page

European foreword 3

1 Scope 4

2 Normative references 4

3 Terms and definitions 4

4 Principle 5

5 Reagents 5

6 Apparatus and equipment 6

7 Sampling and sample preparation 6

7.1 Sampling 6

7.2 Sample preparation 6

8 Procedure 6

8.1 Preparation of the test portion and the sample solution 6

8.2 Calibration of the system (titre factor) 7

8.3 Determination 7

8.4 Control test 7

9 Calculation and expression of the results 7

10 Precision 8

10.1 Inter-laboratory study 8

10.2 Repeatability 8

10.3 Reproducibility 8

11 Test report 9

Annex A (informative) Results of the inter-laboratory study 10

Bibliography 12

European foreword

This document (prEN 17758:2026) has been prepared by Technical Committee CEN/TC 260 “Fertilizers and liming materials”, the secretariat of which is held by DIN.

This document is currently submitted to CEN Enquiry.

This document has been prepared under a standardization request addressed to CEN by the European Commission. The Standing Committee of the EFTA States subsequently approves these requests for its Member States.

prEN 17758:2026 includes the following significant technical changes with respect to CEN/TS 17758:2022:

— The CEN Technical Specification has been adopted as a European Standard;

— Scope (Clause 1) updated regarding the applicability to fertilizing product blends;

— Water as reagent has been included (5.1);

— The option to use a centrifuge for the preparation of test portion (8.1) of organic and organic-mineral fertilizers added;

— The precision data (Clause 10) of the validation study included;

— Annex A including results of inter-laboratory study added;

— Normative references (Clause 2) and Bibliography revised.

This document has been prepared under a standardization request addressed to CEN by the European Commission. The Standing Committee of the EFTA States subsequently approves these requests for its Member States.

This document specifies a method for the determination of the chloride content in organic fertilizers, organo-mineral fertilizers, inorganic fertilizers and liming materials by potentiometric titration.

This document is applicable to fertilizing product blends, where a blend is a mix of at least two of the following components, fertilizers and liming materials, and where the following category, organic fertilizers, organo-mineral fertilizers, inorganic fertilizers or liming materials, is the highest % in the blend by mass or volume, or in the case of liquid form, by dry mass.

If organic fertilizers, organo-mineral fertilizers, inorganic fertilizers, or liming materials is not the highest % in the blend, the European Standard for the highest % of the blend applies. In case a fertilizing product blend is composed of components in equal quantity, the user decides which standard to apply.

NOTE Variations in analytical methods for fertilizing product blends can lead to differing results as some components or matrix interactions can affect the outcome. Validation procedures have shown that developed standard methods are robust and reliable across diverse product compositions, but possible interferences and unexpected results when analysing fertilizing product blends are possible.

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.

EN 1482‑2, Fertilizers, liming materials and inhibitors — Sampling and sample preparation — Part 2: General sample preparation provisions

EN 12944‑1,^[1] Fertilizers, liming materials and inhibitors — Vocabulary — Part 1: General terms

EN 12944‑2,^[2] Fertilizers, liming materials and inhibitors — Vocabulary — Part 2: Terms relating to fertilizers

EN 12944‑3, Fertilizers, liming materials and inhibitors — Vocabulary — Part 3: Terms relating to liming materials

For the purposes of this document, the terms and definitions given in EN 12944‑1, EN 12944‑2 and EN 12944‑3 apply.

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

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/

The chlorides, dissolved in water, are precipitated in an acidified medium by a standard solution of silver nitrate. The chloride concentration in the samples is quantified by potentiometric determination. To detect the end point, the voltage between a reference electrode on the one hand and the silver electrode or an ion selective electrode on the other hand, is tracked. This voltage depends on the logarithm of the chloride ion activity. If it is plotted, in mV, on the ordinate and the silver nitrate solution, in ml, on the abscissa, the point of inflection of the curve obtained in this manner is the equivalence point. Equivalent methods of evaluation are permitted [4, 6].

Use only reagents of recognized analytical grade.

5.1 Water, distilled or demineralized with a specific conductivity not higher than 0,2 mS/m at 25 °C, free from chloride.

5.2 Nitric acid, substance concentration c = 16 mol/l.

5.3 Nitric acid solution, c = 10 mol/l.

Mix 630 ml of nitric acid (5.2) with 370 ml of water.

5.4 Silver nitrate standard solution, c = 0,1 mol/l.

Stock solution or preparation from AgNO₃ salt; since this salt is hygroscopic and cannot be dried without risk of decomposition, it is advisable to weigh out approximately 17 g, dissolve in water and fill up the volume to 1 l.

A commercially available silver nitrate standard solution may be used.

5.5 Polyvinyl alcohol (PVA) solution, acidified with nitric acid.

Mix 2 g of polyvinyl alcohol with 400 ml of hot water (approx. 90 °C; 5.1) in a 1 000 ml graduated flask and let it cool to room temperature. Add 10 ml of nitric acid solution (5.3) and fill up with water (5.1) to 1 000 ml.

It is recommended to use an acidified protector colloid medium for the potentiometric titration (8.2 and 8.3).

5.6 Sodium chloride standard solution, c = 0,100 mol/l.

A commercially available sodium chloride standard solution may be used.

5.7 Sodium chloride control test sample, c = 0,017 mol/l

Prepare a control test sample by dissolving 0,989 1 g ± 0,000 1 g of sodium chloride in 1 000 ml demineralized water (5.1) and homogenize the solution. This control test sample contains 0,6 g/l chloride.

Usual laboratory glassware and equipment, in particular, the following.

6.1 Heat plate, with stirrer or laboratory shaker.

6.2 Pipettes.

6.3 Graduated flask, capacity 500 ml.

6.4 Beaker, capacity 250 ml.

6.5 Potentiometric titration system, incl. millivolt meter and burette or other liquid handling/dosing unit; optional incl. motoric stirrer.

6.6 Silver electrode or ion selective electrode, for chloride.

6.7 Reference electrode, with chloride-free salt bridge.

NOTE A combined electrode which includes both, ion selective and reference electrode, can be used.

6.8 Balance, capable of weighing to the nearest 0,000 1 g.

6.9 Filter paper, pore size 0,45 µm, free of chloride.

6.10 pH testing device, e.g. pH meter, pH indicator paper, or pH rapid test.

Sampling is not part of the method specified in this document. Recommended sampling methods are given in EN 1482‑1 [1] and EN 1482‑3 [2].

It is important that the laboratory receives a sample that is representative of both the product under consideration and the given analysis. The sample should not have been damaged or changed during transport or storage.

Sample preparation shall be carried out in accordance with EN 1482‑2.

Grinding of the sample is recommended for homogeneity reasons.

Place 5 g to 10 g of the sample, weighed to the nearest 0,001 g, in a graduated flask (6.3) and add 250 ml of water (5.1). Bring to boil and stir while boiling for at least 0,5 h (6.1); after cooling to room temperature fill up to 500 ml with water (5.1); mix and filter (6.9) into a beaker (6.4) or into a flask (6.3).

For samples containing easily water-soluble chloride compounds, the boiling step may be skipped and only homogenization by stirring or shaking is necessary.

The filtration step may be skipped, provided that the sample solution shows little to no precipitates.

Alternatively, sample preparation can be performed according to EN 15958.

For organic and organic-mineral fertilizers it is recommended to alternatively centrifuge the sample solution instead of filtration.

The titre factor of the silver nitrate standard solution (5.4) is determined by titrating 5 ml of sodium chloride standard solution (5.6), diluted with 60 ml of water (5.1) in a beaker. Then add 5 ml of PVA solution (5.5). The titration is repeated three times. By the mean value of the used volume of the silver nitrate standard solution (5.4) calculate the titre factor.

The titre factor shall be calculated according to the manual of the potentiometric titration system (6.5).

NOTE 1 The volumes of the sodium chloride standard solution and the water can be varied, provided that the volume ratio stays constant.

NOTE 2 The determination of the titre factor of commercially available standard solutions is optional but can be notably beneficial.

Take an aliquot part of the sample solution (see 8.1) containing not more than 0,150 g of chloride, e.g. 100 ml. Then add 5 ml of PVA solution (5.5). Test for the pH (6.10) and if the pH of the sample solution is > 2, adjust the pH to < 2 by adding dropwise nitric acid solution (5.3) to the sample solution (see 8.1).

Then add silver nitrate standard solution (5.4) with a burette or comparable liquid dosing unit (6.5). The silver nitrate consumption depends on the chloride content in the sample solution (see 8.1) and shall be between 2 ml and 20 ml, ideally between 5 ml and 10 ml.

The pH shall be adjusted just under pH 2. Adding too much acid can bias the measurement.

If the sample solution (see 8.1) is not filtrated before determination, it is recommended to use a motoric stirrer within the potentiometric titration system (6.5) to prevent a clogging of the electrodes (6.6, 6.7).

Before carrying out the estimations check the accuracy of the method by using an aliquot part of 150 ml of a freshly prepared solution of sodium chloride (5.7). This should result in a mass fraction of chlorides equal to 30 g/kg.

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

Calculate the mass fraction of chlorides (Cl), w_Cl, in g/kg, according to Formula (1).

(1)

where

V_z is the amount of the silver nitrate standard solution (5.4), in ml;

F is the titre factor (8.2) of the silver nitrate standard solution (5.4);

V_a is the volume of the graduated flask used for the sample preparation (6.3), in ml;

m is the mass of the test portion taken (8.1), in g;

V_b is the volume of the sample aliquot taken for determination (8.3), in ml;

M_Cl is the molar mass of chlorine, 35,453 2 g/mol;

c_z is the substance concentration of the silver nitrate standard solution (5.4), in mol/l.

Details of inter-laboratory studies on the precision of the method are summarized in Annex A. Repeatability and reproducibility were calculated according to ISO 5725‑2 [6] and ISO 5725‑3 [7].

It is possible that the values derived from this study are not applicable to concentration ranges and matrices other than those given.

The absolute difference between two independent single test results, obtained using the same method on identical test material in the same laboratory by the same operator using the same equipment within a short interval of time, will in no more than 5 % of the cases be greater than the repeatability limit r given in Table 1.

The absolute difference between two independent single test results, obtained using the same method on identical test material in different laboratories with different operators using different equipment, will in no more than 5 % of the cases be greater than the reproducibility limit R given in Table 1.

Table 1 — Mean values, repeatability and reproducibility limits

The test report shall contain at least the following information:

a) all information necessary for the complete identification of the sample;

b) the test method used with reference to this document (including its year of publication);

c) the test results obtained;

d) date of sampling and sampling procedure (if known);

e) date when the analysis was finished;

f) 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 result(s).

1. 
   (informative)
   
   Results of the inter-laboratory study
   1. Inter-laboratory study

The precision of the method has been determined in the year 2025 in an inter-laboratory study with 11 laboratories participating and carried out on 5 samples of organic, organo-mineral, inorganic fertilizers, and liming materials. The statistical results are given in Table A.1.

The statistical results for the samples are given in Table A.1.

• 1. Statistical results for the determination of chloride by potentiometric titration

Table A.1 — Statistical results for determination of chloride in organic, organo-mineral, inorganic fertilizers, and liming materials

Bibliography

[1] EN 1482‑1, Fertilizers, liming materials and inhibitors — Sampling and sample preparation — Part 1: General sampling provisions

[2] EN 1482‑3, Fertilizers, liming materials and inhibitors — Sampling and sample preparation — Part 3: Sampling of static heaps

[3] EN 15958, Fertilizers — Extraction of water soluble phosphorus

[4] EN 16195, Fertilizers — Determination of chlorides in the absence of organic material

[5] DIN 38405‑1, Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung; Anionen (Gruppe D); Bestimmung der Chlorid-Ionen (D 1)

[6] ISO 5725‑2, Accuracy (trueness and precision) of measurement methods and results - Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method

[7] ISO 5725‑3, Accuracy (trueness and precision) of measurement methods and results - Part 3: Intermediate precision and alternative designs for collaborative studies

1. Under revision. Stage at the time of preparation: prEN 12944-1:2026 ↑

2. Under revision. Stage at the time of preparation: prEN 12944-2:2026 ↑