FprEN 18258

SLOVENSKI STANDARD
01-december-2025
Izboljševalci tal in rastni substrati - Določanje živega srebra
Soil improvers and growing media - Determination of the mercury content
Bodenverbesserungsmittel und Kultursubstrate - Bestimmung von Quecksilber in
Königswasser-Extrakten
Amendements du sol et supports de culture - Détermination de la teneur en mercure
Ta slovenski standard je istoveten z: prEN 18258
ICS:
65.080 Gnojila Fertilizers
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
prEN 18258
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2025
ICS 65.080
English Version
Soil improvers and growing media - Determination of the
mercury content
Amendements du sol et supports de culture - Bodenverbesserungsmittel und Kultursubstrate -
Détermination de la teneur en mercure Bestimmung von Quecksilber in Königswasser-
Extrakten
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 18258:2025 E
worldwide for CEN national Members.

prEN 18258:2025 (E)
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 5
4.1 Vapour generation atomic absorption spectrophotometry (VG-AAS) . 5
4.2 Thermal decomposition, amalgamation and atomic absorption spectrophotometry (AAS)
(TD-AAS). 5
5 Interferences . 6
5.1 Vapour generation atomic absorption spectrophotometry (VG-AAS) . 6
5.2 Thermal decomposition, amalgamation and atomic absorption spectrophotometry (AAS)
(TD-AAS). 6
6 Reagents . 6
7 Apparatus . 7
8 Sampling . 7
9 Procedure . 8
9.1 Preparation of the test and blank solutions . 8
9.2 Preparation of the calibration solutions . 8
9.3 Measurement . 8
9.3.1 Instrument conditions . 8
9.3.2 Matrix effects . 8
9.3.3 Spiking . 9
9.3.4 Measurement by VG-AAS . 9
9.3.5 Measurement by TD-AAS. 9
10 Calculation and expression of the results . 10
10.1 Content of mercury. 10
11 Test report . 11
12 Validation of the method . 11
12.1 Validation in accordance with ISO 5725-2. 11
12.2 Performance characteristics. 11
Annex A (informative) Methods for mercury determination . 12
Annex B (informative) Performance characteristics of the method . 14
Bibliography . 16

prEN 18258:2025 (E)
European foreword
This document (prEN 18258:2025) has been prepared by Technical Committee CEN/TC 223 “Soil
improvers and growing media”, the secretariat of which is held by NEN.
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.
prEN 18258:2025 (E)
Introduction
This document concerns the analytical measurement step for the determination of mercury in soil
improvers and growing media after digestion by aqua regia according to prEN 13650:2025or directly by
thermal decomposition, amalgamation and atomic absorption spectrophotometry (AAS). The document
covers cold vapour generation followed by mercury determination using atomic absorption
spectrophotometry (AAS). Different cold vapour generation techniques can be used (flow injection,
segmented flow, batch). The document also includes a direct method based on thermal decomposition,
amalgamation and AAS which is widely used in many analytical laboratories. It is also possible to use
other suitable methods of mercury determination described in Annex A, if users prove that the methods
give the same results as the methods described in this document.
prEN 18258:2025 (E)
1 Scope
This document specifies a method for determination of mercury in aqua regia digests of soil improvers
and growing media, prepared according to prEN 13650:2025, using (cold) vapour generation apparatus
coupled to an atomic absorption spectrophotometer or thermal decomposition, amalgamation and
atomic absorption spectrophotometry. With the latter technique, direct analysis is also suitable for solid
samples.
NOTE 1 It is also possible to use other suitable methods for the determination of mercury described in Annex A
if users prove that the method gives the same results as the methods described in this document.
NOTE 2 In unique circumstances where mercury is bound in silicates or other matrices (e.g. phosphates) that do
not thermally decompose, it is essential to validate direct analysis of the solid using the aqua regia digestion
according to prEN 13650:2025, followed by analysis with this method (see Clause 5.2).
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
prEN 13650:2025, Soil improvers and growing media — Digestion by aqua regia for subsequent
determination of elements
3 Terms and definitions
For the purposes of this document the terms and definitions given in CEN/TS 17732:2022 apply.
4 Principle
4.1 Vapour generation atomic absorption spectrophotometry (VG-AAS)
Mono- and divalent mercury is reduced to the elemental form by tin(II) chloride or sodium borohydride
in an acid medium. Elemental mercury is stripped off from the solution and determined in the form of an
atomic gas by an atomic absorption spectrophotometer.
4.2 Thermal decomposition, amalgamation and atomic absorption spectrophotometry
(AAS) (TD-AAS)
The sample is thermally decomposed in an oxygen rich environment. The decomposition products are
carried to an amalgamator that selectively traps mercury. After the system is flushed with oxygen to
remove any remaining gases or decomposition products, the amalgamator is rapidly heated, releasing
mercury vapour. Flowing oxygen carries the mercury vapour through absorbance cells positioned in the
light path of a single wavelength atomic absorption spectrophotometer. Absorbance is measured at
253,7 nm as a function of mercury concentration.
prEN 18258:2025 (E)
5 Interferences
5.1 Vapour generation atomic absorption spectrophotometry (VG-AAS)
The matrix of the solution analysed is dominated by the acids used in the digestion step. Tin(II) chloride
as a reduction substance is recommended, because sodium borohydride reduces many elements
commonly found in organic fertilizers and organo-mineral fertilizers digests to the elemental state, which
may cause matrix problems under particular circumstances. However, it is still possible to use sodium
borohydride as a reduction agent. The interferences due to the presence of other elements in the matrix
depend on its concentrations. Copper, manganese and nickel exceeding a concentration of 500 mg/l can
cause a negative bias.
5.2 Thermal decomposition, amalgamation and atomic absorption spectrophotometry
(AAS) (TD-AAS)
Instruments with an amalgamation technique are very often used for a direct determination of mercury
in samples without a digestion step. Nevertheless, some solid samples (e.g. samples with a very high
silicates or phosphate content) might not be fully thermally decomposed and therefore in this case or if
an unknown sample is analysed, the analysis of aqua regia digests is preferable. For organic fertilizers
and organo-mineral fertilizers usually no difference is observed between the direct determination of
mercury and the determination of mercury after digestion in aqua regia.
6 Reagents
The concentration of mercury in the reagents and in water shall be negligible compared to the lowest
concentration of mercury to be determined.
6.1 Water with a specific conductivity not higher than 0,2 mS/m at 25 °C.
6.2 Carrier gas.
Argon or nitrogen for VG-AAS and VG-ICP-OES, oxygen for TD-AAS, purity according to the
recommendation of the manufacturer.
6.3 Hydrochloric acid, c(HCl) ≈ 12 mol/l; 37 % volume fraction; mass concentration ρ approximately
1,18 g/ml.
6.4 Nitric acid, c(HNO ) ≈ 16 mol/l; not less than 65 % volume fraction; ρ approximately 1,42 g/ml.
6.5 Mixed acid solution, 0,8 mol/l nitric acid and 1,8 mol/l hydrochloric acid.
Mix 150 ml of hydrochloric acid (6.3) and 50 ml nitric acid (6.4) to 1,0 l of water.
6.6 Reducing agents
Tin(II) chloride or sodium borohydride may be used as the reducing agent, but it is not advisable to use
the two reagents alternately. Follow the instructions of the manufacturers of the apparatus. The
concentration by mass of the reducing agent solutions may be varied to suit the system, and the relevant
information provided by the manufacturer of the apparatus shall be observed.
6.6.1 Tin(II) chloride solution, ρ (SnCl ∙ 2 H O) = 100 g/l
2 2
Dissolve 10 g of SnCl ∙ 2 H O in 30 ml of hydrochloric acid (6.3), transfer to a 100 ml volumetric flask and
2 2
fill to the mark with water. The blank concentration of mercury can be reduced by bubbling a stream of
nitrogen through the solution for 30 min, if necessary. Prepare this solution on the day of use.
6.6.2 Sodium borohydride solution, NaBH , ρ (NaBH ) = 30 g/l
4 4
prEN 18258:2025 (E)
1 g sodium hydroxide, NaOH, is weighed into a 100 ml volumetric flask and dissolved in water. Three g
sodium borohydride, NaBH , are weighed into a 100 ml volumetric flask, dissolved and diluted to the
mark with the sodium hydroxide solution.
A solution of lower concentration, e.g. 3 g/l may be used with flow systems. Prepare this solution freshly
on the day of use from the more concentrated solution by diluting with water. Follow the
recommendations of the manufacturer of the instrument.
WARNING – It is essential to observe the safety instructions for working with sodium borohydride.
Sodium borohydride forms hydrogen with acids and this can result in an explosive air/hydrogen mixture.
A permanent fume extraction system shall be provided at the point where measurements are carried out.
6.7 Standard stock solution, ρ = 1 000 mg/l
Use commercially available mercury stock solution with adequate specification, stating the acid used and
the preparation technique. The solution is considered to be stable for more than one year, but in reference
to guaranteed stability, see the recommendations of the manufacturer. Alternatively, the stock solutions
may be prepared by the dissolution of high purity metal mercury or its salts.
6.7.1 Standard solution I, ρ = 100 mg/l
Pipette 10 ml of the mercury standard stock solution (6.7) into a 100 ml volumetric flask. Add 10 ml of
nitric acid (6.4), fill to the mark with water and mix well. This solution is stable for one month.
6.7.2 Standard solution II, ρ = 1 mg/l
Pipette 1 ml of mercury standard solution I (6.7.1) into a 100 ml volumetric flask. Add 10 ml of nitric acid
(6.4) fill to the mark with water and mix well. This solution is stable for 7 days.
6.7.3 Standard solution III, ρ = 100 µg/l
Pipette 10 ml of mercury standard solution II (6.7.2) into a 100 ml volumetric flask. Add 10 ml of nitric
acid (6.4) fill to the mark with water and mix well. This solution shall be freshly prepared on the day of
use.
7 Apparatus
The instruments 7.2 and 7.3 are used for the VG-AAS method.
7.1 Common laboratory glassware.
7.2 Atomic absorption spectrophotometer, equipped with a heated quartz cell and an element
specific lamp for mercury.
7.3 Vapour generation system. The system should be adaptable to the atomic absorption
spectrophotometer (7.2). Batch or continuous systems (segmented flow or flow-injection) may be used.
The settings of the working conditions shall be optimized according to the manufacturer’s instructions.
7.4 Mercury analyser, with combustion, amalgamation and measurement capabilities.
8 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.
prEN 18258:2025 (E)
9 Procedure
9.1 Preparation of the test an
...