ISO/FDIS 15936

• Abstract:

  Specifies a method for the determination of the total carbon content in soil after dry combustion. The organic carbon content is calculated from this content after correcting for carbonates present in the sample. If carbonates are removed beforehand, the organic carbon content is measured directly. Applicable to all types of air-dried soil samples.

• Status: Not Published
• ICS: 13.080.10 - Chemical characteristics of soils
• Technical Committee: ISO/TC 190/SC 3 - Chemical and physical characterization
• Drafting Committee: ISO/TC 190/SC 3/WG 1 - Inorganic analysis
• Current Stage: 5000 - FDIS registered for formal approval
• Start Date: 17-Jul-2026
• Completion Date: 16-Apr-2026

• Consolidates: prEN ISO 15936 - Soil, waste, treated biowaste and sludge - Determination of total organic carbon (TOC) by dry combustion (ISO/DIS 15936:2025)
• Effective Date: 12-Feb-2026
• Consolidates: ISO/TR 12231-2:2022 - Photography — Electronic still picture imaging terminology — Part 2: Other defined terms
• Effective Date: 17-May-2025
• Revises: ISO 10694:1995 - Soil quality — Determination of organic and total carbon after dry combustion (elementary analysis)
• Effective Date: 07-Jan-2025

Overview

ISO/FDIS 15936:2026 specifies standardized procedures for the determination of total organic carbon (TOC) in soil, waste, treated biowaste, and sludge using dry combustion. The standard details both an indirect (Method A) and a direct (Method B) method to quantify TOC, considering the need to correct for inorganic carbonates present in the sample. This method is suitable for air-dried soil samples with more than 0.1% carbon in relation to the dry matter, supporting consistent, reliable results in environmental quality and waste management contexts.

Key Topics

• Total Organic Carbon (TOC) Determination: The central focus is the accurate measurement of TOC, which serves as an important indicator for soil and waste quality.
• Dry Combustion Methods: Utilizes high-temperature combustion and subsequent analysis of released carbon dioxide to quantify carbon content.
• Correction for Carbonates: Differentiates organic from inorganic carbon through separate quantification or prior removal of carbonates.
• Sample Preparation: Specifies air-drying and particle size requirements to ensure homogeneity and representative analysis.
• Calibration and Quality Control: Outlines procedures for calibration, control measurements, and calculation of results, ensuring traceability and reproducibility.
• Reporting Requirements: Defines the minimum information to be included in test reports, supporting transparency and comparability.
• Applicability: Suitable for a wide range of matrices, including soils, treated biowaste, sludge, and various types of waste.

Applications

The standardized procedures in ISO/FDIS 15936:2026 are essential across several sectors:

• Environmental Monitoring: Measurement of TOC helps assess soil health, monitor remediation processes, and evaluate waste treatment effectiveness.
• Agriculture: TOC content supports soil fertility assessments and sustainable land management practices.
• Waste Management: Determining TOC in waste and sludge informs classification, recycling, and disposal strategies, meeting regulatory compliance.
• Research and Laboratories: Environmental and geotechnical laboratories use these methods for soil and waste characterization in research and policy development.
• Site Remediation: TOC analysis supports the evaluation of contaminated land and the progress of bioremediation projects.

Related Standards

To ensure comprehensive soil and waste analysis, ISO/FDIS 15936 should be used alongside related standards such as:

• ISO 10694: Previous standard for determination of organic and total carbon after dry combustion (now merged with ISO/FDIS 15936).
• EN 15936: European equivalent, now harmonized under this international standard.
• ISO 11464: Soil quality - Pre-treatment of samples for physicochemical analysis.
• EN 16179, EN 15002: Standards for the preparation of waste and sludge samples.

Practical Value

Implementing ISO/FDIS 15936:2026 provides numerous practical benefits:

• Consistent Results: Promotes reliability and comparability of TOC data across laboratories and countries.
• Environmental Compliance: Supports organizations in meeting regulatory and legislative requirements concerning soil and waste characterization.
• Quality Assurance: Standardized calibration and control measures reduce analytical errors and enhance confidence in reported values.
• Informed Decision-Making: Accurate TOC data inform land management, waste disposal, and remediation strategies, leading to better environmental outcomes.

By following ISO/FDIS 15936:2026, stakeholders ensure robust, harmonized determination of total organic carbon, underpinning key environmental assessments and facilitating sound policy and management decisions related to soil, waste, treated biowaste, and sludge.

FINAL DRAFT
International
Standard
ISO/TC 190/SC 3
Soil, waste, treated biowaste and
Secretariat: DIN
sludge — Determination of total
Voting begins on:
organic carbon (TOC) by dry
2026-09-29
combustion
Voting terminates on:
2026-11-24
Sols, déchets, biodéchets traités et boues — Dosage du carbone
organique total (COT) par combustion sèche
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 SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/CEN PARALLEL PROCESSING LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 190/SC 3
Soil, waste, treated biowaste and
Secretariat: DIN
sludge — Determination of total
Voting begins on:
organic carbon (TOC) by dry
combustion
Voting terminates on:
Sols, déchets, biodéchets traités et boues — Dosage du carbone
organique total (COT) par combustion sèche
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 SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/CEN PARALLEL PROCESSING
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
4.1 Method A (indirect procedure) .2
4.2 Method B (direct procedure) .2
5 Interferences . 2
6 Reagents . 3
7 Apparatus . 4
8 Sample pre-treatment . 4
9 Procedure – Method A (indirect method) . 4
9.1 Determination .4
9.1.1 General .4
9.1.2 Determination of the TC .4
9.1.3 Determination of the TIC .5
9.2 Calibration .5
9.3 Control measurements .5
9.4 Calculation and expression of results .6
10 Procedure ‒ Method B (direct method) . 7
10.1 Determination .7
10.1.1 General .7
10.1.2 Removal of the inorganic carbon and determination of the TOC . .7
10.2 Calibration .8
10.3 Control measurements .8
10.4 Calculation and expression of results .9
11 Performance data . 9
12 Expression of results . 9
13 Test report . 9
Annex A (informative) Repeatability and reproducibility data .11
Annex B (informative) Factors influencing dry combustion methods . 14
Bibliography . 17

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO’s adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3, Chemical
and physical characterization, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 444, Environmental characterization of solid matrices, in accordance with the
Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
The first edition of ISO 15936 edition cancels and replaces ISO 10694:1995, which has been technically
revised.
The main changes are as follows:
— the content of EN 15936:2022 and ISO 10694:1995 has been merged;
— the scope has been widened to include treated biowaste, waste and sludge;
— the indirect method for the TOC determination has been added (method A);
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
FINAL DRAFT International Standard ISO/FDIS 15936:2026(en)
Soil, waste, treated biowaste and sludge — Determination of
total organic carbon (TOC) by dry combustion
WARNING — Persons using this document should be familiar with usual laboratory practice. This
document does not purport to address all of the safety problems, if any, associated with its use. It is
the responsibility of the user to establish appropriate safety and health practices.
IMPORTANT — The tests conducted according to this document shall be carried out by suitably
trained staff.
1 Scope
This document specifies two methods for the determination of total organic carbon (TOC) in sludge, treated
biowaste, soil and waste samples containing more than 0,1 % carbon in relation to the dry matter (dm).
This document is validated for sludge, biowaste, soil, and waste (see also Annex A for the results of the
validation).
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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/
3.1
total carbon
TC
quantity of carbon present in the sample in the form of organic, inorganic and elemental carbon
3.2
total inorganic carbon
TIC
quantity of carbon that is liberated as carbon dioxide by acid treatment
Note 1 to entry: Typically, the TIC represents the carbonates present in a sample.
3.3
total organic carbon
TOC
quantity of carbon that is converted into carbon dioxide by combustion and which is not liberated as carbon
dioxide by acid treatment
4 Principle
4.1 Method A (indirect procedure)
In this procedure, the TOC is obtained by the difference between the results of the measurements of TC and
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 or modifiers, or
both, can be used. The released amount of carbon dioxide is measured 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 is measured by one of the techniques mentioned above.
4.2 Method B (direct procedure)
In this procedure, the TIC present in the sample is previously removed by treating the sample with acid,
using the method described in 10.1.2. The carbon dioxide released by the following combustion step is
measured by one of the techniques mentioned in 4.1 and indicates the TOC directly.
NOTE The quality of results of Method B is dependent on experience and practice, especially regarding the steps
before the determination of TOC. Use of automatic dispensing units regarding removal of TIC prior to determination of
TOC can improve the performance of Method B.
5 Interferences
Depending on the laboratory experience with samples containing high amounts of TIC, the procedures can
lead to unreliable TOC results if the TIC to TOC ratio is very high (e.g. ≥ 10).
Depending on the detection method used, different interferences can occur, for instance:
— the presence of cyanide can interfere with the coulometric detection of TIC by modifying the pH value
[dissolution of hydrogen cyanide (HCN)];
— high content of halogenated compounds can lead to an underestimation of TIC when coulometric
detection is used and so an overestimation of calculated TOC; in some cases, the classical silver or copper
trap can be insufficient to absorb all halides.
Method B can lead to incorrect results in the following cases.
— Volatile organic substances (e.g. volatile hydrocarbons from sludge of oil separators) can be lost during
sample preparation especially during the acidification. If necessary, the carbon content resulting from
volatile organic substances shall be determined separately.
— Side reactions between the sample and the acid take place (e.g. decarboxylation, volatile reaction
products).
When present, elemental carbon, carbides, cyanides, cyanates, isocyanates, isothiocyanates and thiocyanates
are determined as organic carbon using the methods described in this document. An interpretation of the
measured value can 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.
Depending on the method of detection used, reagents or catalysts, or both, may be required for reduction,
oxidation, removal and/or fixing of combustion gases which interfere with the analysis. These reagents and/
or chemicals shall be used according to the manufacturer’s instruction.

6 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified.
Hygroscopic substances shall be stored in a desiccator.
6.1 Calcium carbonate, CaCO .
6.2 Sodium carbonate, Na CO , anhydrous.
2 3
6.3 Tetrasodium ethylenediamine tetraacetate-tetra-hydrate, Na -EDTA ∙ 4 H O (C H N O Na ∙
4 2 10 12 2 8 4
4 H O), heated at 80 °C for 2 h.
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 6.10 and 6.11).
6.4 Potassium hydrogen phthalate, C H O K.
8 5 4
6.5 Acetanilide, C H NO.
8 9
6.6 Atropine, C H NO .
17 23 3
6.7 Spectrographic graphite powder, C.
6.8 Sodium salicylate, C H O Na.
7 5 3
6.9 Aluminium oxide, Al O , neutral, granular size < 200 µm, annealed at 600 °C.
2 3
6.10 Control mixture A, prepared from sodium carbonate (6.2), Na -EDTA ∙ 4 H O (6.3) and aluminium
4 2
oxide (6.9) in a mass ratio of 2,34 : 1,00 : 7,28.
The mixture shall be homogenized. It shall contain 2,5 % TIC and 2,5 % TOC (e.g. 22,06 g of sodium carbonate,
9,41 g Na -EDTA ∙ 4 H O, 68,53 g of aluminium oxide).
4 2
Depending on the matrix of interest and manufacturer instructions, control mixtures with higher TIC and
TOC contents may be used additionally.
6.11 Control mixture B, prepared from sodium salicylate (6.8), calcium carbonate (6.1), Na -EDTA · 4 H O
4 2
(6.3) and aluminium oxide (6.9) in a mass ratio of 1,00 : 4,36 : 1,97 : 8,39.
The mixture shall be homogenized. It shall contain 3,3 % TIC and 6,6 % TOC (e.g. 6,36 g of sodium salicylate,
27,78 g of calcium carbonate, 12,50 g of Na4-EDTA · 4 H O, 53,36 g of aluminium oxide).
Depending on the matrix of interest and manufacturer instructions, control mixtures with higher TIC and
TOC contents may be used additionally.
6.12 Non-oxidizing mineral acid, used for carbon dioxide expulsion, e.g. phosphoric acid H PO (w =
3 4
85 %) or sulfurous acid H SO .
3 4
NOTE Due to potential corrosion by hydrochloric acid, phosphoric acid is preferred for TIC determination in
Method A (9.1.3). Due to potential formation of P O during combustion, hydrochloric acid is preferred for removal of
4 10
inorganic carbon in Method B (10.1.2).
6.13 Carrier gas, e.g. synthetic air, nitrogen, oxygen, argon or helium, free of carbon dioxide and organic
impurities in accordance with the manufacturer’s instructions.

6.14 Ethylenediaminetetraacetic acid (EDTA), C H N O .
10 16 2 8
6.15 Glycine, C H NO .
2 5 2
7 Apparatus
7.1 Precision balance, accurate to at least 0,5 % of test portion weight.
7.2 Equipment for determination of carbon in solids, with relevant accessories.
7.3 Purging unit for TIC determination, for Method A only.
7.4 Vessels, made of e.g. ceramic, silica, quartz, silver or platinum.
Tin and nickel vessels are not acid-resistant. Tin vessels are suitable only for Method A. If using sulfurous
acid, nickel boat liners may be used in combination with e.g. ceramic vessels.
8 Sample pre-treatment
Moist or paste-like waste samples may be mixed with aluminium oxide (6.9) until granular material is
obtained and then be ground or crushed to a maximum particle size (D ) ≤ 250 μm. In this case, the ratio of
aluminium oxide to sample shall be considered in the calculation of TOC (according to 9.4 or 10.4).
NOTE 1 For waste samples, the homogeneity is important and often the aluminium oxide step is helpful. More
information is given in Annex B.
All other samples should be pre-treated according to EN 16179 or EN 15002 or ISO 11464 or ISO PWI 21744,
if not otherwise specified. The maximum particle size (D ) shall be ≤ 250 μm. Foreign bodies or material
that can’t be ground or crushed should be separated from the sample and the weight and nature of the
material should be recorded.
NOTE 2 D is the so-called percentile value. It is a statistical parameter that can be read directly from the
cumulative particle size distribution. It indicates the size below which 95 % of all particles are found.
Samples shall be dried. If moist or paste-like waste samples contain – depending on the accuracy requested
for the method – negligible amounts of volatile compounds except water, the samples shall be also dried. The
drying temperature should not exceed 40 °C. The drying method shall be recorded.
NOTE 3 The drying method can affect the result.
9 Procedure – Method A (indirect method)
9.1 Determination
9.1.1 General
The mass of the test portion shall 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 or calibration.
9.1.2 Determination of the TC
To minimize carbon blank values the vessel may be pre-treated by heating (in a muffle furnace or the TC
apparatus itself). The sample prepared according to Clause 8 is weighed into a suitable vessel (7.4).
The sample is combusted or decomposed in a flow of carrier gas containing oxygen (6.13).

The combustion temperature shall be high enough to convert all carbon completely to carbon dioxide.
NOTE For samples containing carbonates, which are difficult to decompose, e.g. barium carbonate, the release
of the carbon dioxide can be improved by increasing the temperature or by the use of modifiers, e.g. tin, copper (see
Clause B.1).
The temperature range of commercially available instruments is between 900 °C and 1 500 °C.
During the combustion of reactive samples, explosion or fuming can be prevented by covering the sample
with inert material e.g. silica sand.
The amount of carbon dioxide released during the combustion is measured e.g. by infrared spectrometry,
thermal conductivity detection, or other suitable techniques, and is expressed as total carbon (TC).
9.1.3 Determination of the TIC
The sample prepared according to Clause 8 is weighed into the purging unit (7.3) or i
...

ISO/TC 190/SC 3
Secretariat: DIN
Date: 2026-07-0809-14
Soil, waste, treated biowaste and sludge – — Determination of total
organic carbon (TOC) by dry combustion
Sols, déchets, biodéchets traités et boues — Dosage du carbone organique total (COT) par combustion sèche
FDIS stage
TThhiis drs draafftt i is s ssuubbmmiitttteedd ttoo aa ppaarraallellel l vvoottee i inn IISSOO,, CCEEN.N.

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents
Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
4.1 Method A (indirect procedure) . 2
4.2 Method B (direct procedure) . 2
5 Interferences . 2
6 Reagents . 3
7 Apparatus . 4
8 Sample pre-treatment . 4
9 Procedure – Method A (indirect method) . 4
9.1 Determination . 4
9.2 Calibration . 5
9.3 Control measurements . 6
9.4 Calculation and expression of results . 6
10 Procedure ‒ Method B (direct method) . 8
10.1 Determination . 8
10.2 Calibration . 8
10.3 Control measurements . 8
10.4 Calculation and expression of results . 9
11 Performance data . 10
12 Expression of results . 10
13 Test report . 10
Annex A (informative) Repeatability and reproducibility data . 11
Annex B (informative) Factors influencing dry combustion methods . 14
Bibliography . 18

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO'sISO’s adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3, Chemical
and physical characterization, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 444, Environmental characterization of solid matrices, in accordance with the
Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
The first edition of ISO 15936 edition cancels and replaces ISO 10694:1995, which has been technically
revised.
The main changes are as follows:
— — the content of EN 15936:2022 and ISO 10694:1995 has been merged;
— — the scope has been widened to include treated biowaste, waste and sludge;
— — the indirect method for the TOC determination has been added (method A);
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
FINAL DRAFT International Standard ISO/FDIS 15936:2026(en)

Soil, waste, treated biowaste and sludge – — Determination of total
organic carbon (TOC) by dry combustion
WARNING — Persons using this document should be familiar with usual laboratory practice. This
document does not purport to address all of the safety problems, if any, associated with its use. It is
the responsibility of the user to establish appropriate safety and health practices.
IMPORTANT — The tests conducted according to this document shall be carried out by suitably trained
staff.
1 Scope
This document specifies two methods for the determination of total organic carbon (TOC) in sludge, treated
biowaste, soil and waste samples containing more than 0,1 % carbon in relation to the dry matter (dm).
This document is validated for sludge, biowaste, soil, and waste (see also Annex AAnnex A for the results of
the validation).
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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/
3.1 3.1
total carbon
TC
quantity of carbon present in the sample in the form of organic, inorganic and elemental carbon
3.2 3.2
total inorganic carbon
TIC
quantity of carbon that is liberated as carbon dioxide by acid treatment
Note 1 to entry: Typically, the TIC represents the carbonates present in a sample.
3.3 3.3
total organic carbon
TOC
quantity of carbon that is converted into carbon dioxide by combustion and which is not liberated as carbon
dioxide by acid treatment
4 Principle
4.1 Method A (indirect procedure)
In this procedure, the TOC is obtained by the difference between the results of the measurements of TC and
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 or modifiers, or both,
can 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 is measured by one of the techniques mentioned above.
4.2 Method B (direct procedure)
In this procedure, the TIC present in the sample is previously removed by treating the sample with acid, using
the method described in 10.1.210.1.2. The carbon dioxide released by the following combustion step is
measured by one of the techniques mentioned in 4.14.1 and indicates the TOC directly.
NOTE The quality of results of Method B is dependent on experience and practice, especially regarding the steps
before the determination of TOC. Use of automatic dispensing units regarding removal of TIC prior to determination of
TOC can improve the performance of Method B.
5 Interferences
Depending on the laboratory experience with samples containing high amounts of TIC, the procedures can
lead to unreliable TOC results if the TIC to TOC ratio is very high (e.g. ≥ 10).
Depending on the detection method used, different interferences can occur, for instance:
— — the presence of cyanide can interfere with the coulometric detection of TIC by modifying the pH value
[dissolution of hydrogen cyanide (HCN)];
— — high content of halogenated compounds can lead to an underestimation of TIC when coulometric
detection is used and so an overestimation of calculated TOC; in some cases, the classical silver or copper
trap can be insufficient to absorb all halides.
Method B can lead to incorrect results in the following cases:.
— — Volatile organic substances (e.g. volatile hydrocarbons from sludge of oil separators) can be lost during
sample preparation especially during the acidification. If necessary, the carbon content resulting from
volatile organic substances shall be determined separately.
— — sideSide reactions between the sample and the acid take place (e.g. decarboxylation, volatile reaction
products).
When present, elemental carbon, carbides, cyanides, cyanates, isocyanates, isothiocyanates and thiocyanates
are determined as organic carbon using the methods described in this document. An interpretation of the
measured value can 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.
Depending on the method of detection used, reagents or catalysts, or both, may be required for reduction,
oxidation, removal and/or fixing of combustion gases which interfere with the analysis. These reagents and/or
chemicals shall be used according to the manufacturer'smanufacturer’s instruction.
6 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified.
Hygroscopic substances shall be stored in a desiccator.
6.1 6.1 Calcium carbonate, CaCO .
6.2 6.2 Sodium carbonate, Na CO , anhydrous.
2 3
6.3 6.3 Tetrasodium ethylenediamine tetraacetate-tetra-hydrate, Na -EDTA ∙ 4 H O
4 2
(C H N O Na ∙ 4 H O), heated at 80 °C for 2 h.
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 6.106.10 and 6.116.11).).
6.4 6.4 Potassium hydrogen phthalate, C H O K.
8 5 4
6.5 6.5 Acetanilide, C H NO.
8 9
6.6 6.6 Atropine, C H NO .
17 23 3
6.7 6.7 Spectrographic graphite powder, C.
6.8 6.8 Sodium salicylate, C H O Na.
7 5 3
6.9 6.9 Aluminium oxide, Al O , neutral, granular size < 200 µm, annealed at 600 °C.
2 3
6.10 6.10 Control mixture A, prepared from sodium carbonate (6.2(6.2),), Na -EDTA ∙ 4 H O (6.3(6.3))
4 2
and aluminium oxide (6.9(6.9)) in a mass ratio of 2,34 : 1,00 : 7,28.
The mixture shall be homogenized. It shall contain 2,5 % TIC and 2,5 % TOC (e.g. 22,06 g of sodium carbonate,
9,41 g Na -EDTA ∙ 4 H O, 68,53 g of aluminium oxide).
4 2
NOTE Depending on the matrix of interest and manufacturer instructions, control mixtures with
higher TIC and TOC contents may be used additionally.
6.11 6.11 Control mixture B, prepared from sodium salicylate (6.8(6.8),), calcium carbonate
(6.1(6.1),), Na -EDTA · 4 H O (6.3(6.3)) and aluminium oxide (6.9(6.9)) in a mass ratio of 1,00 : 4,36 : 1,97 :
4 2
8,39.
The mixture shall be homogenized. It shall contain 3,3 % TIC and 6,6 % TOC (e.g. 6,36 g of sodium salicylate,
27,78 g of calcium carbonate, 12,50 g of Na4-EDTA · 4 H O, 53,36 g of aluminium oxide).
NOTE Depending on the matrix of interest and manufacturer instructions, control mixtures with
higher TIC and TOC contents may be used additionally.
6.12 6.12 Non-oxidizing mineral acid, used for carbon dioxide expulsion, e.g. phosphoric acid H PO (w
3 4
= 85 %) or sulfurous acid H SO .
3 4
NOTE Due to potential corrosion by hydrochloric acid, phosphoric acid is preferred for TIC determination in
Method A (9.1.3(9.1.3).). Due to potential formation of P4O10 during combustion, hydrochloric acid is preferred for
removal of inorganic carbon in Method B (10.1.2(10.1.2).).
6.13 6.13 Carrier gas, e.g. synthetic air, nitrogen, oxygen, argon or helium, free of carbon dioxide and
organic impurities in accordance with the manufacturer'smanufacturer’s instructions.
6.14 6.14 Ethylenediaminetetraacetic acid (EDTA), C H N O .
10 16 2 8
6.15 6.15 Glycine, C H NO .
2 5 2
7 Apparatus
7.1 7.1 Precision balance, accurate to at least 0,5 % of test portion weight.
7.2 7.2 Equipment for determination of carbon in solids, with relevant accessories.
7.3 7.3 Purging unit for TIC determination, for Method A only.
7.4 7.4 Vessels, made of e.g. ceramic, silica, quartz, silver or platinum.
NOTE Tin and nickel vessels are not acid-resistant. Tin vessels are suitable only for Method A. If using
sulfurous acid, nickel boat liners may be used in combination with e.g. ceramic vessels.
8 Sample pre-treatment
Moist or paste-like waste samples may be mixed with aluminium oxide (6.9(6.9)) until granular material is
obtained and then be ground or crushed to a maximum particle size (D ) ≤ 250 μm. In this case, the ratio of
aluminium oxide to sample shall be considered in the calculation of TOC (according to 9.49.4 or 10.410.4).).
Note NOTE 1 For waste samples, the homogeneity is important and often the aluminium oxide step is helpful. More
information is given in Annex BAnnex B.
All other samples should be pre-treated according to EN 16179 or EN 15002 or ISO 11464 or ISO PWI 21744,
if not otherwise specified. The maximum particle size (D ) shall be ≤ 250 μm. Foreign bodies or material that
can’t be ground or crushed should be separated from the sample and the weight and nature of the material
should be recorded.
NOTE 2 D95 is the so-called percentile value. It is a statistical parameter that can be read directly from the cumulative
particle size distribution. It indicates the size below which 95 % of all particles are found.
Samples shall be dried. If moist or paste-like waste samples contain – depending on the accuracy requested
for the method – negligible amounts of volatile compounds except water, the samples shall be also dried. The
drying temperature should not exceed 40 ˚C °C. The drying method shall be recorded.
NOTE 3 The drying method can affect the result.
9 Procedure – Method A (indirect method)
9.1 Determination
9.1.1 General
The mass of the test portion shall 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 or calibration.
9.1.2 Determination of the TC
To minimize carbon blank values the vessel may be pre-treated by heating (in a muffle furnace or the TC
apparatus itself). The sample prepared according to Clause 8Clause 8 is weighed into a suitable vessel
(7.4(7.4).).
The sample is combusted or decomposed in a flow of carrier gas containing oxygen (6.13(6.13).).
The combustion temperature shall be high enough to convert all carbon completely to carbon dioxide.
NOTE For samples containing carbonates, which are difficult to decompose, e.g. barium carbonate, the release of the
carbon dioxide can be improved by increasing the temperature or by the use of modifiers, e.g. tin, copper (see
Clause B.1B.1).).
The temperature range of commercially available instruments is between 900 °C and 1 500 °C.
During the combustion of reactive samples, explosion or fuming can be prevented by covering the sample with
inert material e.g. silica sand.
The amount of carbon dioxide released during the combustion is measured e.g. by infrared spectrometry,
thermal conductivity detection, or other suitable techniques, and is expressed as total carbon (TC).
9.1.3 Determination of the TIC
The sample prepared according to Clause 8Clause 8 is weighed into the purging unit (7.3(7.3)) or in the sample
vessel (7.4(7.4).).
The system is closed gas-tight and flushed with carrier gas until no more carbon dioxide from ambient air is
present. Then acid (6.12(6.12)) is added and the carbon dioxide is stripped by purging or stirring, by heating,
or both. The released carbon dioxide is transferred to the detector by the carrier gas.
The addition of wetting agents, e.g. surfactants, can improve wetting of the surface of the sample.
The addition of anti-foaming agents, e.g. silicone oil, can be helpful in the case of strongly foaming samples.
The amount of carbon dioxide released during the gas evolution is measured e.g. by infrared spectrometry,
thermal conductivity detection, or other suitable techniques and is expressed as total inorganic carbon (TIC).
Samples containing persistent carbonates (e.g. concrete, cement) require treatment with hot acid for complete
release of carbon dioxide according to manufacturers'manufacturers’ instructions.
9.2 Calibration
If a relative method is used for detection, e.g. infrared detection, calibration is necessary. Calibration shall be
performed according to the manufacturer'smanufacturer’s instruction.
Examples of calibration substances suitable for TC are calcium carbonate (6.1(6.1),), potassium hydrogen
phthalate (6.4(6.4),), acetanilide (6.5(6.5),), atropine (6.6(6.6),), spectrographic graphite powder (6.7(6.7),),
EDTA (6.14(6.14),), glycine (6.15(6.15).).
The following procedure shall be applied for calibration:
— — Establish the preliminary working range.
— — Measure a minimum of five standard samples. Typically, different sample weights of one calibration
substance are used to cover the calibration range. The absolute amount of carbon of these standard
samples shall be distributed evenly over the requested working range.
— — Calculate the calibration function according to manufacturer'smanufacturer’s instruction for TC and
TIC.
— — Use the calibration function for calculating the mean values of the recovery of each standard sample.
9.3 Control measurements
Control measurements shall be carried out using control mixture A (6.10(6.10)) for the procedures according
to 9.1.29.1.2 (TC) and 9.1.39.1.3 (TIC). For the control measurements, analysis of two sample weights of the
control
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