FprEN 18257

SLOVENSKI STANDARD
oSIST prEN 18257:2025
01-december-2025
Izboljševalci tal in rastni substrati - Določanje kroma Cr(VI)
Soil improvers and growing media - Determination of chromium(VI)
Bodenverbesserungsmittel und Kultursubstrate - Bestimmung von Chrom(VI)
Amendements du sol et supports de culture - Détermination du chrome(VI)
Ta slovenski standard je istoveten z: prEN 18257
ICS:
65.080 Gnojila Fertilizers
oSIST prEN 18257:2025 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN 18257:2025
oSIST prEN 18257:2025
DRAFT
EUROPEAN STANDARD
prEN 18257
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2025
ICS 65.080
English Version
Soil improvers and growing media - Determination of
chromium(VI)
Amendements du sol et supports de culture - Bodenverbesserungsmittel und Kultursubstrate -
Détermination du chrome(VI) Bestimmung von Chrom(VI)
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 223.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 18257:2025 E
worldwide for CEN national Members.

oSIST prEN 18257:2025
prEN 18257:2025 (E)
Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Principle . 4
5 Reagents . 5
6 Apparatus . 5
7 Sampling . 6
8 Procedure . 6
8.1 Preparation of analytical solution . 6
8.1.1 Solid and shear resistant pasty samples . 6
8.1.2 Liquid and aqueous pasty samples . 7
8.2 Chromatographic conditions . 7
8.3 Calibration . 7
8.4 Determination of the recovery rate . 8
9 Calculation and expression of results . 8
9.1 Calculation of chromium(VI) content . 8
9.2 Recovery rate (according to 8.4) . 9
9.3 Expression of results . 9
10 Test report . 9
11 Validation of the method . 10
11.1 Validation in accordance with ISO 5725-2. 10
11.2 Performance characteristics. 10
Annex A (informative) Chromatographic conditions for direct detection method . 11
Annex B (informative) Chromatographic conditions for method with post-column reaction . 14
Annex C (informative) Performance characteristics of the method . 18
Bibliography . 21

oSIST prEN 18257:2025
prEN 18257:2025 (E)
European foreword
This document (prEN 18257:2025) has been prepared by Technical Committee CEN/TC 223 “Soil
improvers and growing media”, the secretariat of which is held by NEN, in collaboration with CEN/TC 260
“Fertilizers and liming materials” and CEN/TC 455 “Plant Biostimulants”.
This document is currently submitted to the 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.
oSIST prEN 18257:2025
prEN 18257:2025 (E)
1 Scope
This document specifies a method for the determination of hexavalent chromium (CrVI) in soil improvers
and growing media.
The method described is suitable to quantify the Cr(VI) content in soil improvers and growing media
down to 1 mg/kg dry matter.
NOTE Samples with a low dry matter content can have an influence on the achievable limit of quantification as
defined in the scope.
The results obtained from this method are strictly dependent on the extraction conditions. Results
obtained by using other extraction procedures (extraction solution, pH of the extraction solution,
extraction time, extraction temperature, etc.) are not comparable with the results produced by the
procedure described in this document.
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.
CEN/TS 17732:2022, Soil improvers and growing media - Terminology
EN 12579:2024, Soil improvers and growing media - Sampling
prEN 13040-1:2025, Soil improvers and growing media — Sample preparation — Part 1: Sample
preparation for chemical and physical tests, determination of dry matter content, moisture content and
laboratory bulk density
3 Terms and definitions
For the purposes of this document, the terms and definitions given in CEN/TS 17732:2022 and the
following apply.
3.1
chromium(VI) content
amount of chromium(VI) in soil improvers and growing media determined after extraction with an
aqueous salt solution at pH 7,0 to pH 8,0
Note 1 to entry: The chromium(VI) content is reported as chromium(VI) in milligrams per kilogram (mg/kg),
expressed as the dry mass of the sample.
[SOURCE: EN ISO 17075-2:2017, 3.1, modified: “leather” is replaced by “soil improvers and growing
media” and “pH 7,0 to 8,0” is replaced by “pH 7,0 to pH 8,0”]
4 Principle
Extractable Cr(VI) is leached from the sample in phosphate buffer at pH 7,0 to pH 8,0. An aliquot of the
filtered extract, or its dilution, is analysed for Cr(VI) using ion-exchange chromatography with UV-VIS
detection.
A preliminary determination of the total chromium in aqua regia extracts by ICP-AES (prEN 13650:2025)
can reduce the number of the samples where the determination of chromium(VI) is necessary because if
the content of aqua regia (total) extractable chromium is lower than the legislative limit for chromium(VI)
then the determination of chromium(VI) may be omitted.
oSIST prEN 18257:2025
prEN 18257:2025 (E)
5 Reagents
All reagents used shall have at least analytical grade.
5.1 Extraction solution
Dissolve 22,8 g dipotassium hydrogen phosphate K HPO ·3H O in 1 000 ml water (5.7), adjusted to
2 4 2
pH 8,0 ± pH 0,1 with phosphoric acid (5.2). Degas this solution with either argon or nitrogen (5.6) or
ultrasonic bath.
Standard practice is to make up a fresh solution each day. However, the solution may be kept for up to
one week in a refrigerator at (4 ± 3) °C but shall be warmed to room temperature and degassed prior to
use.
5.2 Phosphoric acid solution
700 ml o-phosphoric acid, density ρ = 1,71 g/ml, made up to 1 000 ml with water (5.7).
First add approximately 200 ml of deionised water (5.7) to a 1 000 ml volumetric flask, then add the
700 ml of o-phosphoric acid and dilute to the mark with deionised water.
5.3 Potassium dichromate (K Cr O ), dried for 16 h ± 2 h at 105 °C ± 2 °C.
2 2 7
5.4 Chromium(VI) stock solution
Dissolve 2,829 g potassium dichromate (K Cr O ) (5.3) in water (5.7) in a volumetric flask and make up
2 2 7
to 1 000 ml with water (5.7). One ml of this solution contains 1 mg of chromium.
Commercially available stock solutions at this concentration level of hexavalent chromium may be used
for the same purpose.
5.5 Chromium(VI) standard solution
Pipette 1 ml of solution (5.4) into a 1 000 ml volumetric flask and make up to the mark with extraction
solution (5.1). One ml of this solution contains 1 μg of chromium.
The solution may be kept for up to one week in a refrigerator at 4 °C ± 3 °C but shall be warmed to room
temperature prior to use.
Commercially available stock solutions at this concentration level of hexavalent chromium may be used
for the same purpose.
5.6 Argon or nitrogen, oxygen-free
Preference should be given to argon as an inert gas instead of nitrogen because argon has a higher specific
mass than air.
5.7 Distilled or deionised water, with a specific conductivity not higher than 0,2 mS/m at 25 °C, free
from the elements to be determined.
5.8 Magnesium chloride hexahydrate (MgCl ·6H O)
2 2
Dissolve 85,4 g in a 100 ml volumetric flask, dilute with water (5.7), close and mix thoroughly.
6 Apparatus
Usual laboratory equipment and, in particular, the following.
−1 −1
6.1 Suitable mechanical orbital shaker, 100 min ± 10 min .
oSIST prEN 18257:2025
prEN 18257:2025 (E)
6.2 Conical flask, of capacity 250 ml, with stopper.
6.3 Aeration tube and flow meter, suitable for a flow rate of (50 ± 10) ml/min.
6.4 pH meter, with glass electrode.
6.5 Membrane filter, 0,45 μm pore size [polytetrafluoroethylene (PTFE) or polyamide 66].
6.6 Common laboratory glassware and pipettes.
6.7 Vacuum device, suitable for filtration of extraction solution, mobile phase, and sample extracts.
6.8 Ion-exchange chromatograph, with UV detector or high-performance liquid
chromatography (HPLC) with anion-exchange column and UV detector. A photo diode array
detector (DAD) is recommended.
6.9 Analytical balance, capable of weighing to 0,1 mg.
6.10 Syringe membrane filters of nylon, 0,45 μm pore size, for filtration of standards.
6.11 Suitable vials for HPLC.
7 Sampling
Sampling is not part of the method specified in this document. EN 12579:2024 shall be followed dealing
with soil improvers and growing media. It is important that the laboratory receives a sample that is
representative of the product under consideration. The sample should not have been damaged or
changed during transport or storage.
8 Procedure
8.1 Preparation of analytical solution
8.1.1 Solid and shear resistant pasty samples
The operator shall weigh (6.9) approximately 10 g ± 0,1 g of fresh sample of soil improvers and growing
media to the nearest 0,01 g.
A higher sample intake may be considered for coarse samples to keep the liquid to solid ratio during the
extraction.
Following tasks shall be performed:
— Pipette 100 ml (V ) of degassed solution (5.1) into a 250 ml conical flask (6.2). If the sample is
expected to contain a significant amount of chromium(III), 1 ml of magnesium chloride solution (5.8)
may be added. Displace oxygen by passing oxygen-free argon (or nitrogen) (5.6) into the flask.
Remove the aeration tube (6.3), add the sample and close the flask with a stopper.
— Shake the conical flask with the sample for 30 min on a mechanical orbital shaker at
−1 −1
± 10 min (6.1) at room temperature to extract the Cr(VI).
100 min
— Shake the suspension in a smooth circular movement to keep the sample from adhering to the wall of
the flask and avoid shaking faster than specified.
Immediately after completing the 30 min of extraction, filter the contents of the conical flask through a
membrane filter into a glass or plastic vessel with lid. Check the pH of the solution. The pH of the
oSIST prEN 18257:2025
prEN 18257:2025 (E)
solution shall be between 7,0 and 8,0. If the pH of the solution is not within this range, start the
complete procedure again and consider using a smaller sample mass. If filtration is not possible in a
30 min period, centrifugation may be applied prior to filtration.
— Transfer an aliquot of the filtered extract, or its dilution, into a vial (6.11). Instrumental determination
of Cr(VI) should be performed as soon as possible and within a day after the extraction phase to avoid
risks of reduction.
8.1.2 Liquid and aqueous pasty samples
The operator shall weigh (6.9) approximately 10 g ± 0,1 g of sample of soil improvers and growing media
to the nearest 0,01 g.
The following tasks shall be performed:
— Pipette 100 ml (V0) of degassed solution (5.1) into a 250 ml conical flask (6.2). If the sample is
expected to contain a significant amount of chromium(III), 1 ml of magnesium chloride solution (5.8)
may be added. Displace oxygen by passing oxygen-free argon (or nitrogen) (5.6) into the flask.
Remove the aeration tube (6.3), add the sample and close the flask with a stopper.
— Shake the conical flask with the sample for 10 min ± 1 min on a mechanical orbital shaker at
−1 −1
100 min ± 10 min (6.1) at room temperature to extract the Cr(VI).
— Shake the suspension in a smooth circular movement to keep the sample from adhering to the wall of
the flask and avoid shaking faster than specified.
— Immediately after completing the 10 min of extraction, filter the contents of the conical flask through
a membrane filter into a glass or plastic vessel with lid. Check the pH of the solution. The pH of the
solution shall be between 7,0 and 8,0. If the pH of the solution is not within this range, start the
complete procedure again and consider using a smaller sample mass. If filtration is not possible in a
30 min period, centrifugation may be applied prior to filtration.
— Transfer an aliquot of the filtered extract, or its dilution, into a vial (6.11). Instrumental determination
of Cr(VI) should be performed as soon as possible and within a day after the extraction phase to avoid
risks of reduction.
8.2 Chromatographic conditions
Determination of Cr(VI) is performed using the ion chromatographic technique. As the instrumental
equipment of the laboratories may vary, no specific applicable instructions can be provided for analysis.
However, the operating parameters and examples of the ion chromatographic analysis for Cr(VI) listed
in Annex A and Annex B have been successfully tested and used. Annex A determines Cr(VI) by direct
detection of chromate peak at 372 nm. Annex B determines Cr(VI) after a post-column reaction with 1,5-
diphenylcarbazide by measuring the absorption peak at 540 nm.
The method used should be verified using the recovery rate determination (8.4).
Record the injection volume as V and record the area of the chromate peak as A.
M
8.3 Calibration
The content of Cr(VI) in the sample of soil improvers and growing media is determined with an external
standard calibration.
The operator shall prepare calibration solutions from the standard solution (5.5). The Cr(VI)
concentration in these solutions should cover the expected range of measurement.
The following tasks shall be performed:
oSIST prEN 18257:2025
prEN 18257:2025 (E)
— Plot a suitable calibration curve by using at least five standards. Pipette the given volumes of standard
solution (5.5) into volumetric flasks. Make up to volume with the extraction solution or its dilution
(5.1), mix well, filter (6.10) and transfer a suitable aliquot volume into a vial (6.11).
— Transfer an aliquot to a suitable vial (6.11) corresponding for the chromatographic system (6.8).
— Inject the standards in the chromatographic system (6.8). Introduce the same volume for each
standard. It is recommended to inject equal volume for samples. Record the volume injected as V in
c
μl.
— Plot the Cr(VI) concentrations in micrograms of chromium per millilitre (μg/ml) against the
measured areas of the peaks of chromate. Plot the Cr(VI) concentration on the x-axis and the area on
the y-axis.
8.4 Determination of the recovery rate
Verify the method by preparing a soluble Cr(VI) standard solution from a stock standard solution from a
different source than that used for preparing the calibration
...