CEN/TC 260

Date: 2025-10

prEN 15957:2025

Secretariat: DIN

Inorganic fertilizers — Extraction of phosphorus which is soluble in neutral ammonium citrate

Anorganische Düngemittel - Extraktion des in neutralem Ammoniumcitrat löslichen Phosphors

Engrais inorganiques — Extraction du phosphore soluble dans du citrate d’ammonium neutre

CCMC will prepare and attach the official title page.

Contents Page

European foreword 3

1 Scope 4

2 Normative references 4

3 Terms and definitions 4

4 Principle 4

5 Sampling and sample preparation 4

6 Reagents 4

7 Apparatus 5

8 Procedure 5

8.1 Test portion 5

8.2 Extraction 5

9 Test report 6

Bibliography 7

European foreword

This document (prEN 15957:2025) 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 will supersede EN 15957:2011.

This document includes the following significant technical changes with respect to EN 15957:2011:

a) characteristics of distilled water added;

b) reference to Regulation (EC) No 2003/2003 removed.

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 extraction of phosphorus soluble in neutral ammonium citrate in inorganic fertilizers.

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, Fertilizers and liming materials — Vocabulary — Part 1: General terms

EN 12944-2, Fertilizers and liming materials — Vocabulary — Part 2: Terms relating to fertilizers

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

ISO and IEC maintain terminology 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/

Extraction of phosphorus at a temperature of 65 °C using a neutral ammonium citrate solution of pH = 7 under the specified conditions.

Sampling is not part of the method specified in this document. A recommended sampling method is given in EN 1482-1.

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 laboratory sample is recommended for homogeneity reasons.

Use only reagents of recognized analytical grade and distilled or demineralized water.

6.1 Water, distilled or demineralized.

The electrical conductivity of distilled or demineralized water used in the analysis shall at least be < 0,5 mS/m (at 25 °C).

6.2 Neutral ammonium citrate solution, pH = 7, containing 185 g crystallized citric acid per litre, specific gravity 1,09 at 20 °C.

Prepare the reagent as follows:

Dissolve 370 g of crystalline citric acid (C₆H₈O₇∙H₂O) in about 1,5 l of water and make an approximately neutral solution by adding 345 ml of ammonium hydroxide solution (28 % to 29 % of NH₃). If the NH₃ concentration is lower than 28 % add a correspondingly larger quantity of ammonium hydroxide solution and dilute the citric acid in correspondingly smaller quantities of water.

Cool and make exactly neutral by keeping the electrodes of a pH-meter immersed in the solution. Add the ammonia, at 28 % to 29 % of NH₃, drop by drop, stirring continuously (with a mechanical stirrer) until obtaining exactly a pH of 7 at a temperature of 20 °C. At this point make up the volume to 2 l and check the pH again. Keep the reagent in a closed container and check the pH at regular intervals.

NOTE The neutral ammonium citrate solution at pH 7,0 is also commercially available.

7.1 Beaker, capacity 2 l.

7.2 pH-meter.

7.3 Erlenmeyer flask, capacity 200 ml or 250 ml.

7.4 Graduated flasks, capacity 500 ml and 2 000 ml.

7.5 Water bath, thermostatically adjustable to (65 ± 2) °C, equipped with a shaking device suitable for Erlenmeyer flasks (7.3)

7.6 Dry pleated filter, medium speed, phosphate free.

Transfer 1 g or 3 g of the laboratory sample to be analysed into a 200 ml or 250 ml Erlenmeyer flask (7.3) containing 100 ml of ammonium citrate solution (6.2) previously heated to 65 °C

Stopper the Erlenmeyer flask (7.3) and shake in order to suspend the test portion without forming lumps. Remove the stopper for an instant in order to balance the pressure and close the Erlenmeyer flask again. Place the flask in a water bath (7.5) set to maintain the contents of the flask at exactly 65 °C and connect it to the stirrer. During stirring, the level of the suspension in the flask shall stay constantly below the level of the water in the water bath. If a mechanical stirrer is not available, the flask may be shaken by hand every 5 min.

Regulate mechanical stirring to ensure complete suspension.

After stirring for exactly 1 h, remove the Erlenmeyer flask from the water bath.

Cool immediately under running water to ambient temperature and, immediately, quantitatively transfer the contents from the Erlenmeyer flask into a graduated 500 ml flask (7.4) with a jet of water (wash bottle). Make up the volume with water. Mix thoroughly. Filter through a dry pleated filter (7.6) into a dry container, discarding the first part of the filtrate (about 50 ml).

Collect about 100 ml of clear filtrate.

The test report shall contain at least the following information:

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

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

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

d) date when the extraction was finished;

e) 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).

Bibliography

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