kSIST FprEN 18253:2026

• Abstract:

  This document specifies a method for the determination of total organic carbon (TOC) in soil improvers and growing media containing more than 1 g carbon per kg of dry matter (0,1 %).; NOTE 1 Samples with a low dry matter content can have an influence on the achievable limit of quantification as defined in the scope (i.e. 1 g carbon per kg of dry matter).; NOTE 2 This method has been validated in an interlaboratory study with specific products that were present on the market during the study (as included in Annex b, being composted bark (20 mm to 40 mm), biowaste compost (Rottegrad 3), green compost (Rottegrad 5,0 mm to 15 mm), solid digestate, liquid digestate, soil improver (pellets, sieved 4 mm) and growing media blend 1 (white peat, green compost, wood fibre, lime, inorganic fertilizer (NPK + micro elements))).

• Status: Not Published
• Public Enquiry End Date: 19-Dec-2025
• ICS: 65.080 - Fertilizers
• Technical Committee: KAT - Soil quality
• Current Stage: 5020 - Formal vote (FV) (Adopted Project)
• Start Date: 09-Oct-2026
• Due Date: 27-Nov-2026
• Directive: 2003/2003 - Regulation (EC) N° 2003/2003 of the European Parlament and of the council of 13 October 2003 relating to fertilisers
• Directive:

  ---

  2019/1009 - Regulation (EU) 2019/1009 of the European Parliament and of the Council of 5 June 2019 laying down rules on the making available on the market of EU fertilising products and amending Regulations (EC) No 1069/2009 and (EC) No 1107/2009 and repealing Regulation (EC) No 2003/2003 (Text with EEA relevance)
• Mandate: M/564 - Fertilising products in support of Regulation (EU) 2019/1009
• Mandate: M/564 AMD 1 - amending Implementing Decision C(2020) 612 as regards certain harmonised standards and standardisation deliverables, deadlines for their adoption and the duration of the validity of the standardisation request
• Mandate: M/564 AMD 2 - Commission Implementing decision amending Implementing Decision C(2020)612 as regards harmonised standards, the deadlines for the adoption of those standards and the duration of the validity of the standardisation request to the European Committee for Standardisation as regards the EU fertilising products in support of Regulation (EU) 2019/1009 of the European Parliament and of the Council
• Mandate: M/588 - COMMISSION IMPLEMENTING DECISION of 20.9.2022 on a standardisation request to the European Committee for Standardisation as regards methods for the measurements of emissions into the air of polychlorinated dibenzo-pdioxins and furans (PCDDs/PCDFs) and dioxin-like polychlorinated biphenyls (PCBs), total gaseous mercury and formaldehyde in support of Directive 2010/75/EU of the European Parliament and of the Council
• Mandate: M/XXX - M/XXX
• Ref Project: FprEN 18253 - Soil improvers and growing media - Determination of total organic carbon (TOC) by dry combustion

kSIST FprEN 18253:2026 is a draft standard for soil improvers and growing media published under the SIST/CEN process. It specifies a dry-combustion method for determining total organic carbon (TOC) in products with more than 1 g carbon per kg of dry matter, for laboratories and technical staff who need comparable test results.

What does kSIST FprEN 18253:2026 specify?

kSIST FprEN 18253:2026 specifies how to determine TOC in soil improvers and growing media and sets the applicability threshold at more than 1 g carbon per kg of dry matter. It also points users to the sampling and sample-preparation standards that sit around the test method, so the laboratory can start from a representative, workable sample.

The document is organized in clauses on scope, normative references, terms and definitions, principle, reagents, apparatus, sampling, procedure, calculation and expression of results, test report, and validation. It has two informative annexes.

Annex	What it covers
Annex A	Example of operational information, including sample preparation, instrument setup, sample mass, crucibles, gases and detectors
Annex B	Performance characteristics from the interlaboratory study, including the materials tested and precision data

What are the key requirements of kSIST FprEN 18253:2026?

kSIST FprEN 18253:2026 gives two routes for TOC measurement: Method A, a direct method, and Method B, an indirect method. In practice, this means a laboratory can either remove inorganic carbon first and measure the remaining carbon dioxide, or measure total carbon and subtract inorganic carbon.

Sample preparation and applicability

Solid samples are dried and ground below 0,5 mm according to the cited sample-preparation standard, while liquid samples are homogenized before weighing. For moist or paste-like solids, the document allows mixing with aluminium oxide to obtain a granular material, but the dilution factor must then be included in the calculation. This matters because sample handling changes the final TOC result if it is not corrected.

Direct determination, Method A

Method A removes inorganic carbon with a non-oxidizing mineral acid before combustion, or uses controlled combustion at 600 °C with a minimum holding time of 220 s. The released carbon dioxide is then measured by infrared spectrometry, thermal conductivity detection, or another suitable detector. In practice, the operator must make sure that carbonate carbon is eliminated or excluded before reporting TOC.

Indirect determination, Method B

Method B determines TOC as the difference between total carbon (TC) and total inorganic carbon (TIC). TC is measured by combustion in an oxygen-containing gas flow free of carbon dioxide, and TIC is measured separately on another sub-sample after acidification and purging. This route is useful when the laboratory already has a validated TIC method and wants to keep the carbonate fraction explicit in the calculation.

Calibration and control

Relative detection systems need calibration over the working range, using at least five standards and a linear calibration function. The document names potassium hydrogen phthalate, acetanilide and atropine as suitable calibration substances, and excludes Na-EDTA for calibration because it is used in control mixtures. Control measurements use a defined control mixture, and the mean recovery should be between 90 % and 110 % with coefficient of variation at or below 5 %.

Interferences, reporting and validation

High-carbonate samples need careful carbonate removal, especially when carbonate content is high relative to TOC. Carbon from urea and urea-condensates carbides is counted as organic carbon by this method, so relevant amounts should be determined separately and recorded in the test report. The report also needs the sample identification, method used, pretreatment, result in g/kg TOC, sampling details if known, and any unusual operating details.

What terms does kSIST FprEN 18253:2026 define?

• Total carbon (TC) - the carbon present in a sample as organic, inorganic and elemental carbon.
• Total organic carbon (TOC) - the organic carbon content determined by this dry-combustion method and reported as carbon.
• Total inorganic carbon (TIC) - the inorganic carbon fraction measured separately when Method B is used.
• Method A (direct method) - the route that removes inorganic carbon before combustion, or uses controlled combustion at 600 °C.
• Method B (indirect method) - the route that calculates TOC from TC minus TIC.
• Control mixture - the check material used to verify recovery and instrument performance.

Who uses kSIST FprEN 18253:2026?

kSIST FprEN 18253:2026 is used by testing laboratories, producers of soil improvers and growing media, and quality-control teams that need TOC data for product characterization. It is also relevant to buyers, specifiers and conformity-assessment bodies that compare products or verify reported composition. The method is especially useful where carbonate content, moisture content and sample form can affect the result.

Which standards are used with kSIST FprEN 18253:2026?

• CEN/TS 17732:2022 - provides the terminology used in the document.
• EN 12579:2024 - covers sampling of soil improvers and growing media.
• prEN 13040-1:2025 - covers sample preparation and the water-content work needed for dry-matter reporting.
• EN ISO 10693:2014 - is named for determining TIC in Method B.
• CEN/TS 17776:2022 - is named as a related dry-combustion reference in the procedure.
• ISO 8466-1 - supports the linear calibration check.
• ISO 5725-2 - is used for method validation and precision data.

What does the kSIST FprEN 18253:2026 document contain?

The document contains the full laboratory method, including reagents, apparatus, sample preparation, combustion conditions, calibration steps and control measurements. Clause 8 gives the operational procedures for solid and liquid samples, and Clause 9 gives the calculation steps for dry-matter reporting. Annex A provides worked operational examples from several laboratory setups, while Annex B gives interlaboratory performance data for seven validated matrices, used for method validation and performance assessment.

SLOVENSKI STANDARD
oSIST prEN 18253:2025
01-december-2025
Izboljševalci tal in rastni substrati - Določanje celotnega organskega ogljika (TOC)
s suhim sežigom
Soil improvers and growing media - Determination of total organic carbon by dry
combustion
Bodenverbesserungsmittel und Kultursubstrate - Bestimmung von organischem
Gesamtkohlenstoff durch trockene Verbrennung
Amendements du sol et supports de culture - Détermination du carbone organique total
par combustion sèche
Ta slovenski standard je istoveten z: prEN 18253
ICS:
65.080 Gnojila Fertilizers
oSIST prEN 18253:2025 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN 18253:2025
oSIST prEN 18253:2025
DRAFT
EUROPEAN STANDARD
prEN 18253
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2025
ICS 65.080
English Version
Soil improvers and growing media - Determination of total
organic carbon by dry combustion
Amendements du sol et supports de culture - Bodenverbesserungsmittel und Kultursubstrate -
Détermination du carbone organique total par Bestimmung von organischem Gesamtkohlenstoff
combustion sèche durch trockene Verbrennung
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 18253:2025 E
worldwide for CEN national Members.

oSIST prEN 18253:2025
prEN 18253:2025 (E)
Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Principle . 4
4.1 Method A (direct method) . 4
4.2 Method B (indirect method) . 5
4.3 Interferences . 5
5 Reagents . 5
6 Apparatus . 6
7 Sampling . 6
8 Procedure . 6
8.1 Sample preparation . 6
8.2 Determination . 7
8.2.1 General. 7
8.2.2 Preparation of solid samples . 7
8.2.3 Preparation of liquid samples . 7
8.2.4 Method A: direct determination of the TOC . 7
8.2.5 Method B: indirect determination of TOC . 8
8.3 Calibration . 8
8.4 Control measurements . 9
9 Calculation and expression of results . 9
10 Test report . 11
11 Validation of the method . 11
11.1 Validation in accordance with ISO 5725-2. 11
11.2 Performance characteristics. 11
Annex A (informative) Example of operational information . 12
Annex B (informative) Performance characteristics of the method . 14
Bibliography . 16

oSIST prEN 18253:2025
prEN 18253:2025 (E)
European foreword
This document (prEN 18253:2025) 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 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 18253:2025
prEN 18253:2025 (E)
1 Scope
This document specifies a method for the determination of total organic carbon (TOC) in soil improvers
and growing media containing more than 1 g carbon per kg of dry matter (0,1 %).
NOTE Samples with a low dry matter content can have an influence on the achievable limit of quantification as
defined in the scope (i.e. 1 g carbon per kg of dry matter).
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
CEN/TS 17776:2022, Organic and organo-mineral fertilizers - Determination of the total organic carbon
(TOC) content by dry combustion
EN ISO 10693:2014, Soil quality - Determination of carbonate content - Volumetric method (ISO
10693:1995)
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
total carbon (TC)
quantity of carbon present in the sample in the form of organic, inorganic and elemental carbon
Note 1 to entry: In agreement with Regulation (EU) 2019/1009 [7], carbon derived from urea and polymers
containing urea are not considered as organic in this document.
[SOURCE: CEN/TS 17732:2022, 3.7.21 modified (note 1 to entry added)]
4 Principle
4.1 Method A (direct method)
The carbon dioxide released by the following combustion in an oxygen containing gas flow free of carbon
dioxide, is measured by infrared spectrometry, thermal conductivity detection, or by the detector
provided by the equipment used. To ensure complete combustion, catalysts and/or modifiers may be
used. The released amount of carbon dioxide indicates the TOC.
The carbonates present in the sample shall be previously removed by treating the sample with acid. The
carbon dioxide released by the following combustion step indicates the TOC directly.
Alternatively, the combustion temperature may be set at 600°C, thus only releasing organically bound
carbon.
oSIST prEN 18253:2025
prEN 18253:2025 (E)
4.2 Method B (indirect method)
TOC is obtained by the difference between the results of the measurements of total carbon and total
inorganic carbon (TIC). The total carbon (TC) present in the sample is converted into carbon dioxide by
combustion in an oxygen containing gas flow free of carbon dioxide. To ensure complete combustion,
catalysts and/or modifiers may be used. The released amount of carbon dioxide is measured e.g. by
infrared spectrometry, thermal conductivity detection, or other suitable techniques.
The TIC is determined separately from another sub-sample by means of acidification and purging of the
released carbon dioxide. The carbon dioxide shall be measured by one of the techniques mentioned
above.
4.3 Interferences
In the case of experience with samples containing high amounts of carbonates (e.g. carbonates to TOC
ratio higher than 10) the operator shall take care to correctly eliminate all the carbonates to make sure
to produce reliable TOC results.
When present, carbon from urea and urea-condensates carbides is determined as organic carbon using
the method described in this document. An interpretation of the measured value may therefore be
problematic in cases where the sample contains relevant levels of the above-mentioned components. If
needed, these components shall be determined separately by means of a suitable validated method and
be recorded in the test report.
5 Reagents
All reagents shall be of recognized analytical grade.
5.1 Potassium hydrogen phthalate, C8H5O4K.
H NO.
5.2 Acetanilide, C8 9
5.3 Atropine, C H NO .
17 23 3
5.4 Sodium salicylate, C H O Na.
7 5 3
5.5 Tetrasodium ethylenediamine tetraacetate-tetra-hydrate, Na
EDTA · 4H O (C H N O Na · 4H O), heated at 80 °C for 2 h.
2 10 12 2 8 4 2
Other forms of Na -EDTA hydrates may be used if the water content is exactly known. In these cases, the
composition of the control mixtures shall be recalculated accordingly (see also 5.8).
NOTE Other certified substances can be used as reference materials as well.
5.6 Aluminium oxide, Al O , neutral, granular size < 200 µm, annealed at 600 °C.
2 3
5.7 Calcium carbonate, CaCO .
5.8 Control mixture.
Control mixture prepared from sodium salicylate (5.4), calcium carbonate (5.7), Na -EDTA · 4H O (5.5)
4 2
and aluminium oxide (5.6) in a mass ratio of 1,00 : 4,36 : 1,97 : 8,40.
The mixture shall be homogenized thoroughly (e.g. fine grinding). It should contain 33,3 g/kg total
inorganic carbon and 66,6 g/kg TOC (e.g. 6,36 g of sodium salicylate, 27,73 g of calcium carbonate, 12,53 g
of Na -EDTA · 4H O, 53,42 g of aluminium oxide).
4 2
oSIST prEN 18253:2025
prEN 18253:2025 (E)
NOTE Other control mixtures can be used provided their suitability is checked.
®1
5.9 Inert absorbent material for determination on fluid samples, e.g. Chromosorb .
5.10 Non-oxidizing mineral acid used for carbon dioxide expulsion, e.g. phosphoric acid H PO
3 4
(w = 85 %).
NOTE Due to possible corrosion by hydrochloric acid, phosphoric acid is preferred.
5.11 Carrier gas, e.g. helium, oxygen or argon, free of carbon dioxide and organic impurities in
accordance with the manufacturer's instructions.
6 Apparatus
6.1. Precision balance, capable of weighing to the nearest 0,5 % of test portion mass.
6.2 Equipment for determination of carbon in solids, with accessories.
6.3 Crucibles, capsules or boats, made of e.g. silver, tin, ceramics or platinum.
Tin and nickel crucibles are not acid-resistant. In case of the necessity to remove inorganic carbon (8.2.4),
silver or ceramics vessels shall be used.
6.4 Pasteur pipettes.
6.5 Drying system, thermostatically controlled and capable of maintaining temperature of
105 °C ± 2 °C.
6.6 Desiccator, with an active drying agent such as silica gel.
6.7 Evaporating dish or crucible, temperature tolerant laboratory vessel with a temperature
resistance of at least 110 °C. Suitable materials are metallic, ceramic, borosilicate glass or quartz,
porcelain, etc.
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 Sample preparation
Solid samples are dried and ground < 0,5 mm according to prEN 13040-1:2025. Liquid samples are
homogenized by thorough mixing before weighing the test portion.

Chromosorb® is an example of a suitable product available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by CEN of this product.
oSIST prEN 18253:2025
prEN 18253:2025 (E)
8.2 Determination
8.2.1 General
The mass of the test portion should be as large as possible and shall be chosen so that the liberated
quantity of carbon dioxide lies within the working range of the equipment and calibration. See example
in Table A.1.
8.2.2 Preparation of solid samples
For solid materials dried samples shall be used.
The operator shall weigh an aliquot of sample prepared according to 8.1 into a suitable vessel (6.3) using
the precision balance (6.1).
Moist or paste-like samples may be mixed with aluminium oxide (5.6) until granular material is obtained
and then be milled and homogenized. In th
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