SIST EN ISO 20236:2022

Water quality - Determination of total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TNb) and dissolved bound nitrogen (DNb) after high temperature catalytic oxidative combustion (ISO 20236:2018)

This document specifies a method for the determination of total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TNb) and dissolved bound nitrogen (DNb) in the form of free ammonia, ammonium, nitrite, nitrate and organic compounds capable of conversion to nitrogen oxides under the conditions described. The procedure is carried out instrumentally.
NOTE       Generally the method can be applied for the determination of total carbon (TC) and total inorganic carbon (TIC), see Annex A.
The method is applicable to water samples (e.g. drinking water, raw water, ground water, surface water, sea water, waste water, leachates).
The method allows a determination of TOC and DOC ≥ 1 mg/l and TNb and DNb ≥ 1 mg/l. The upper working range is restricted by instrument-dependent conditions (e.g. injection volume). Higher concentrations can be determined after appropriate dilution of the sample.
For samples containing volatile organic compounds (e.g. industrial waste water), the difference method is used, see Annex A.
Cyanide, cyanate and particles of elemental carbon (soot), when present in the sample, can be determined together with the organic carbon.
The method is not appropriate for the determination of volatile, or purgeable, organic carbon under the conditions described by this method.
Dissolved nitrogen gas (N2) is not determined.

Wasserbeschaffenheit - Bestimmung des gesamten organischen Kohlenstoffs (TOC), des gelösten organischen Kohlenstoffs (DOC), des gebundenen Stickstoffs (TNb) und des gelösten gebundenen Stickstoffs (DNb) nach katalytischer oxidativer Hochtemperaturverbrennung (ISO 20236:2018)

Dieses Dokument legt ein Verfahren zur Bestimmung des gesamten organischen Kohlenstoffs (TOC) und des gelösten organischen Kohlenstoffs (DOC) fest sowie des gesamten gebundenen Stickstoffs (TNb) und des gelösten gebundenen Stickstoffs (DNb), die in Form von freiem Ammoniak, Ammonium, Nitrit, Nitrat vorliegen oder in organischen Verbindungen, die unter den beschriebenen Bedingungen in Stickstoffoxide umgewandelt werden können. Das Verfahren wird instrumentell durchgeführt.
ANMERKUNG   Grundsätzlich kann das Verfahren für die Bestimmung des gesamten Kohlenstoffs (TC) und des gesamten anorganischen Kohlenstoffs (TIC) angewendet werden (siehe Anhang A).
Das Verfahren ist anwendbar für Wasserproben (z. B. Trinkwasser, Rohwasser, Grundwasser, Oberflächen-wasser, Meerwasser, Abwasser, Sickerwässer).
Das Verfahren erlaubt die Bestimmung von TOC und DOC ≥ 1 mg/l und von TNb und DNb ≥ 1 mg/l. Nach oben ist der Arbeitsbereich durch geräteabhängige Bedingungen (z. B. Injektionsvolumen) begrenzt. Höhere Konzentrationen können nach entsprechender Verdünnung der Probe bestimmt werden.
Bei Proben, die flüchtige organische Verbindungen enthalten (z. B. Industrieabwasser), wird das Differenz-verfahren angewandt (siehe Anhang A).
Cyanid, Cyanat und Partikel aus elementarem Kohlenstoff (Ruß) können, falls in der Probe vorhanden, zusammen mit dem organischen Kohlenstoff erfasst werden.
Das Verfahren eignet sich nicht für die Bestimmung von bei den Bedingungen des Verfahrens flüchtigem oder austreibbarem organischem Kohlenstoff.
Gelöster gasförmiger Stickstoff (N2) wird nicht erfasst.

Qualité de l'eau - Dosage du carbone organique total (COT), carbone organique (COD), azote lié total (TNb) et azote lié dissous (DNb) après combustion oxidatif catalytique à haute temperature (ISO 20236:2018)

Le présent document spécifie une méthode de dosage du carbone organique total (COT), du carbone organique dissous (COD), de l'azote lié total (TNb) et de l'azote lié dissous (DNb) sous la forme d'ammoniac libre, ammonium, nitrites, nitrates et composés organiques pouvant être convertis en oxydes d'azote dans les conditions décrites. La procédure est réalisée au moyen d'instruments.
NOTE            Généralement, cette méthode peut s'appliquer au dosage du carbone total (CT) et du carbone inorganique total (CIT), voir Annexe A.
Cette méthode s'applique aux échantillons d'eau (par exemple, eau destinée à la consommation humaine, eau brute, eau souterraine, eau de surface, eau de mer, eaux usées, lixiviats).
Cette méthode permet le dosage du COT et COD ≥ 1 mg/l et du TNb et DNb ≥ 1 mg/l. Le domaine d'analyse supérieur est restreint par les conditions liées aux instruments (par exemple, volume d'injection). Des concentrations supérieures peuvent être dosées après dilution adéquate de l'échantillon.
Pour les échantillons contenant des composés organiques volatils (par exemple, eaux résiduaires industrielles), la méthode par différence est utilisée, voir Annexe A.
Les cyanures, les cyanates et les particules de carbone élémentaire (suie), s'ils sont présents dans l'échantillon, peuvent être dosés avec le carbone organique.
Cette méthode ne convient pas au dosage du carbone organique volatil ou purgeable dans les conditions décrites par la présente méthode.
L'azote gazeux dissous (N2) n'est pas dosé.

Kakovost vode - Določevanje celotnega organskega ogljika (TOC), raztopljenega organskega ogljika (DOC), celotnega vezanega dušika (TNb) in raztopljenega vezanega dušika (DNb) po katalitskem sežigu pri visoki temperaturi (ISO 20236:2018)

Ta mednarodni standard določa metodo za določevanje celotnega organskega ogljika (TOC), raztopljenega organskega ogljika (DOC) ter za določevanje raztopljenega in posebno vezanega dušika (TNb) v obliki prostega amoniaka, amoniaka, nitrita, nitrata in organskih spojin, ki se lahko pod opisanimi oksidativnimi pogoji pretvorijo v dušikove okside. Postopek se izvaja instrumentalno.
OPOMBA 1: Metodo je v splošnem mogoče uporabiti za določevanje skupnega ogljika (TC) in skupnega anorganskega ogljika (TIC) (glej dodatek A v pregledu).
Metoda se uporablja za vodo (npr. pitno vodo, neobdelano vodo, podtalnico, površinsko vodo, morsko vodo ali odpadno vodo), ki vsebuje suspendiran material z velikostjo delcev ≤ 100 μm (dogovor). Pred vbrizgavanjem zmanjšajte delce velikosti > 100 μm na delce velikosti ≤ 100 μm. Metoda omogoča določevanje celotnega organskega ogljika in raztopljenega organskega ogljika ≥ 1 mg/l C ter raztopljenega in posebno vezanega dušika ≥ 1 mg/l N.
OPOMBA 2: Določitev koncentracij ogljika > 0,3 mg/l do 1 mg/l se uporablja samo v posebnih primerih (npr. pitna voda) pri merjenju z visoko občutljivi instrumenti. Cianid, cianat in delce elementarnega ogljika (saje), kadar so prisotni v vzorcu, je mogoče določiti skupaj z organskim ogljikom. Hlapni ali izprani organski ogljik (VOC, POC) ni določen s to metodo. Raztopljeni dušikov plin ni določen s to metodo. Na splošno je delovno območje omejeno s pogoji, ki so odvisni od instrumentov (npr. vbrizgana količina). Višje koncentracije se lahko določijo po ustreznem redčenju.

General Information

• Status: Withdrawn
• Public Enquiry End Date: 01-Oct-2021
• Publication Date: 12-Dec-2021
• Withdrawal Date: 12-Feb-2025
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: KAV - Water quality
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 13-Feb-2025
• Due Date: 08-Mar-2025
• Completion Date: 13-Feb-2025
• Ref Project: EN ISO 20236:2021 - Water quality - Determination of total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TNb) and dissolved bound nitrogen (DNb) after high temperature catalytic oxidative combustion (ISO 20236:2018)

Relations

• Replaces: SIST EN 12260:2003 - Water quality - Determination of nitrogen - Determination of bound nitrogen (TNb), following oxidation to nitrogen oxides
• Effective Date: 01-Jan-2022
• Replaced By: SIST EN ISO 20236:2025 - Water quality - Determination of total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TNb) and dissolved bound nitrogen (DNb) after high temperature catalytic oxidative combustion (ISO 20236:2024)
• Effective Date: 01-Mar-2025

Standards Content (Sample)

SLOVENSKI STANDARD
01-januar-2022
Nadomešča:
SIST EN 12260:2003
Kakovost vode - Določevanje celotnega organskega ogljika (TOC), raztopljenega
organskega ogljika (DOC), celotnega vezanega dušika (TNb) in raztopljenega
vezanega dušika (DNb) po katalitskem sežigu pri visoki temperaturi (ISO
20236:2018)
Water quality - Determination of total organic carbon (TOC), dissolved organic carbon
(DOC), total bound nitrogen (TNb) and dissolved bound nitrogen (DNb) after high
temperature catalytic oxidative combustion (ISO 20236:2018)
Wasserbeschaffenheit - Bestimmung des gesamten organischen Kohlenstoffs (TOC),
des gelösten organischen Kohlenstoffs (DOC), des gebundenen Stickstoffs (TNb) und
des gelösten gebundenen Stickstoffs (DNb) nach katalytischer oxidativer
Hochtemperaturverbrennung (ISO 20236:2018)
Qualité de l'eau - Dosage du carbone organique total (COT), carbone organique (COD),
azote lié total (TNb) et azote lié dissous (DNb) après combustion oxidatif catalytique à
haute temperature (ISO 20236:2018)
Ta slovenski standard je istoveten z: EN ISO 20236:2021
ICS:
13.060.50 Preiskava vode na kemične Examination of water for
snovi chemical substances
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 20236
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2021
EUROPÄISCHE NORM
ICS 13.060.50 Supersedes EN 12260:2003
English Version
Water quality - Determination of total organic carbon
(TOC), dissolved organic carbon (DOC), total bound
nitrogen (TNb) and dissolved bound nitrogen (DNb) after
high temperature catalytic oxidative combustion (ISO
20236:2018)
Qualité de l'eau - Dosage du carbone organique total Wasserbeschaffenheit - Bestimmung des gesamten
(COT), carbone organique (COD), azote lié total (TNb) organischen Kohlenstoffs (TOC), des gelösten
et azote lié dissous (DNb) après combustion oxidatif organischen Kohlenstoffs (DOC), des gebundenen
catalytique à haute temperature (ISO 20236:2018) Stickstoffs (TNb) und des gelösten gebundenen
Stickstoffs (DNb) nach katalytischer oxidativer
Hochtemperaturverbrennung (ISO 20236:2018)
This European Standard was approved by CEN on 15 November 2021.

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. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists 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, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20236:2021 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
Endorsement notice . 3

European foreword
The text of ISO 20236:2018 has been prepared by Technical Committee ISO/TC 147 "Water quality” of
the International Organization for Standardization (ISO) and has been taken over as EN ISO 20236:2021
by Technical Committee CEN/TC 230 “Water analysis” the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by May 2022, and conflicting national standards shall be
withdrawn at the latest by May 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 12260:2003.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: 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, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 20236:2018 has been approved by CEN as EN ISO 20236:2021 without any modification.

INTERNATIONAL ISO
STANDARD 20236
First edition
2018-09
Water quality — Determination of
total organic carbon (TOC), dissolved
organic carbon (DOC), total bound
nitrogen (TN ) and dissolved bound
b
nitrogen (DN ) after high temperature
b
catalytic oxidative combustion
Qualité de l'eau — Dosage du carbone organique total (COT),
carbone organique (COD), azote lié total (TN ) et azote lié dissous
b
(DN ) après combustion oxidatif catalytique à haute temperature
b
Reference number
ISO 20236:2018(E)
©
ISO 2018
ISO 20236:2018(E)
© ISO 2018
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: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

ISO 20236:2018(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Interferences . 3
5.1 General . 3
5.2 TOC or DOC . . 3
5.3 TN or DN . 4
b b
6 Reagents . 4
7 Apparatus . 6
8 Quality requirements for the analytical system . 8
8.1 System check . 8
8.2 Recovery and variation of replicate determinations for particle processing control
for TOC and TN .8
b
9 Sampling and sample preparation . 8
10 Procedure. 9
10.1 General . 9
10.2 Calibration . 9
10.3 Validity check of the calibration function . 9
10.4 Measurement . 9
10.4.1 General. 9
10.4.2 Determination .10
11 Evaluation .11
12 Expression of results .11
13 Test report .11
Annex A (normative) Determination of TOC and TIC applying the difference method .12
Annex B (informative) Performance data for TOC or DOC and TN or DN .15
b b
Annex C (informative) Alternative detection techniques for TN and DN .17
b b
Bibliography .18
ISO 20236:2018(E)
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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
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 147, Water quality, Subcommittee SC 2,
Physical, chemical and biochemical methods.
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 © ISO 2018 – All rights reserved

ISO 20236:2018(E)
Introduction
Total organic carbon (TOC), dissolved organic carbon (DOC), total bound nitrogen (TN ) and dissolved
b
bound nitrogen (DN ) are an analytical convention, the respective result of which is a parameter used
b
for water quality control purposes. These parameters represent the sum of organically bound carbon
as well as the sum of inorganic and organic nitrogen (but not nitrogen gas), which can be dissolved in
water or bonded to dissolved or suspended matter under specified conditions and, if the sample is not
filtered, includes that associated with suspended matter. It does not give information on the nature of
the substances.
Details of an interlaboratory trial on the performance data for TOC or DOC and TN or DN are given in
b b
Annex B.
INTERNATIONAL STANDARD ISO 20236:2018(E)
Water quality — Determination of total organic carbon
(TOC), dissolved organic carbon (DOC), total bound
nitrogen (TN ) and dissolved bound nitrogen (DN ) after
b b
high temperature catalytic oxidative combustion
WARNING — Persons using this document should be familiar with normal 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 — It is absolutely essential that tests conducted in accordance with this document
be carried out by suitably qualified staff.
1 Scope
This document specifies a method for the determination of total organic carbon (TOC), dissolved
organic carbon (DOC), total bound nitrogen (TN ) and dissolved bound nitrogen (DN ) in the form of
b b
free ammonia, ammonium, nitrite, nitrate and organic compounds capable of conversion to nitrogen
oxides under the conditions described. The procedure is carried out instrumentally.
NOTE Generally the method can be applied for the determination of total carbon (TC) and total inorganic
carbon (TIC), see Annex A.
The method is applicable to water samples (e.g. drinking water, raw water, ground water, surface water,
sea water, waste water, leachates).
The method allows a determination of TOC and DOC ≥ 1 mg/l and TN and DN ≥ 1 mg/l. The upper
b b
working range is restricted by instrument-dependent conditions (e.g. injection volume). Higher
concentrations can be determined after appropriate dilution of the sample.
For samples containing volatile organic compounds (e.g. industrial waste water), the difference method
is used, see Annex A.
Cyanide, cyanate and particles of elemental carbon (soot), when present in the sample, can be
determined together with the organic carbon.
The method is not appropriate for the determination of volatile, or purgeable, organic carbon under the
conditions described by this method.
Dissolved nitrogen gas (N ) is not determined.
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.
ISO 8466-1, Water quality — Calibration and evaluation of analytical methods and estimation of
performance characteristics — Part 1: Statistical evaluation of the linear calibration function
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO 20236:2018(E)
ISO and IEC maintain terminological 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
sum of organically and inorganically bound carbon present in water, including elemental carbon
3.2
total inorganic carbon
TIC
sum of inorganic carbon present in water sample measured under the conditions of this method
Note 1 to entry: TIC is measured as CO originating only from carbonates, hydrogen carbonates and dissolved
carbon dioxide.
3.3
total organic carbon
TOC
sum of organically bound carbon present in water, bonded to dissolved or suspended matter, including
cyanate, thiocyanate and elemental carbon measured under the conditions of this method
Note 1 to entry: Volatile organic carbon cannot be guaranteed to be determined by the method.
Note 2 to entry: Generally, TOC includes organic compounds in water that cannot be purged under the conditions
of this method, also known as non-purgeable organic carbon (NPOC).
3.4
dissolved organic carbon
DOC
sum of organically bound carbon present in water originating from compounds passing through a
membrane filter of 0,45 µm pore size, including cyanate and thiocyanate measured under the conditions
of this method
3.5
total bound nitrogen
TN
b
sum of organically bound and inorganically bound nitrogen present in water or suspended matter
measured under the conditions of this method
3.6
dissolved bound nitrogen
DN
b
sum of organically and inorganically bound nitrogen present in water originating from compounds
passing through a 0,45 µm membrane filter measured under the conditions of this method
4 Principle
Thermal catalytic combustion of the sample containing organic carbon, and inorganic and organic
nitrogen in an oxygen-containing atmosphere at ≥ 680 °C for TOC or DOC and ≥ 720 °C for TN or DN
b b
determinations.
The TOC or DOC determination is carried out in accordance with the direct measurement method.
2 © ISO 2018 – All rights reserved

ISO 20236:2018(E)
Prior to combustion, remove inorganic carbon by acidification and purging with a carrier gas (6.7).
NOTE Platinum and cerium(IV), for example, can be used as catalyst material for combustion. The catalyst
serves to accelerate the oxidation process of carbon containing water constituents in excess of oxygen to
produce the required carbon dioxide gas for the detection process. Depending on combustion temperature
and temperatures in the combustion zone, different catalysts can be used, e.g. metals or metal oxides for
temperatures > 680 °C or sintered Alumina for temperatures around 1 200 °C, according to verifications of
different suppliers.
Oxidation of organic carbon (TOC, DOC) with oxygen or synthetic air to carbon dioxide. Detection by
means of infrared spectrometry (IR). Combustion of inorganic and organic nitrogen with oxygen or
synthetic air and conversion to nitric oxide.
Reaction with ozone giving electronically excited nitrogen oxides. Detection by means of
chemiluminescence (CLD) (see Annex C for alternative detection).
This document can be applied for the determination of TOC or DOC and TN or DN separately or for
b b
simultaneous TOC or DOC and TN or DN determinations, for example connecting the IR detector with
b b
a CLD in series.
Quality control is necessary to check the validity of the calibration function (see 10.3). Replicate
determinations can be necessary. The method of standard addition can be required if matrix
interferences are expected (see 5.3 and 10.4.2.1).
5 Interferences
5.1 General
Interferences with the determination of TOC or DOC and TN or DN can arise from memory effects.
b b
Replicate injections are necessary (see 10.4.1).
Detergents, oils and fats can influence the surface tension of the sample, causing erroneous data. A
dilution of the sample can reduce such risk.
Samples with extreme pH values, highly buffered samples and samples with high salt contents can
cause interference. Seek advice from the manufacturer to solve these interferences.
Suspended material can lead to a loss of quality of the analytical result. If a homogenized sample
containing suspended material produces results obtained from replicate measurements that deviate by
more than 10 %, an accurate TOC or TN result cannot be obtained on the sample.
b
5.2 TOC or DOC
Inorganic carbon (e.g. CO or ions of carbonic acid) present in the sample interferes with the
determination of TOC or DOC. Inorganic carbon is removed by acidification and purging with a gas
that is free from CO and organic compounds prior to the TOC or DOC determination (see 10.4.2.2 and
10.4.2.3).
NOTE 1 Alternatively, the differential method determining the TC and TIC separately can be applied
(see Annex A). The TOC can be calculated by subtracting TIC from the TC. This calculation leads to correct results
only as long as carbon monoxide, cyanide, cyanate and thiocyanate are present with negligible concentrations.
NOTE 2 Purgeable organic carbon substances, such as benzene, toluene, cyclohexane and chloroform,
can partly escape upon stripping (see 10.4.2.2 and 10.4.2.3). In the presence of these substances, the TOC
concentration can be determined separately, for example by applying the differential method (see Annex A).
ISO 20236:2018(E)
5.3 TN or DN
b b
High loads of dissolved or total organic carbon (DOC or TOC) can lead to poor recovery of TN or DN .
b b
Suspected problems can be identified by determining nitrogen before and after suitable dilution, or by
using standard addition techniques.
Not all organic nitrogen compounds are quantitatively converted to nitrogen oxide by the combustion
procedure described, and consequently to nitrogen dioxide by the reaction with ozone. Poor recoveries
can occur with compounds containing either double- or triple-bonded nitrogen atoms. The use of
a calibration function calculated in accordance with 10.2 and applying a nitrogen mixed standard
solution II (6.9.3.4) can result in a negative TN bias for ammonium-N determinations (e.g. ammonium
b
sulfate solution) and a positive bias for nitrate-N determinations (e.g. potassium nitrate solution).
6 Reagents
Use reagents of pro analysis grade, if available.
Dry all solid reagents for at least 1 h at (105 ± 5) °C. Store the dried solid in a desiccator before weighing.
NOTE It is not necessary to dry cellulose before usage.
Prepare alternative concentrations and volumes of solutions as described hereafter, if necessary.
Alternatively, use commercially available stock solutions of the required concentration.
When applying the simultaneous determination of TN and TOC, an appropriate mixture of the
b
1 000 mg/l TOC and TN stock solutions (6.8.2 and 6.9.3.3) for the preparation of standard and
b
calibration solutions can be used.
6.1 Water.
The contents of carbon and bound nitrogen in water used for the preparation of samples and solutions
shall be sufficiently low to be negligible in comparison with the lowest TOC and TN concentration to
b
be determined.
6.2 Sulfuric acid, ρ = 1,84 g/ml.
6.3 Hydrochloric acid, ω(HCl) = 32 %.
6.4 Nicotinic acid, C H NO , > 99,5 %.
6 5 2
6.5 TOC and TN stock solution for system check.
b
Place 8,793 g of nicotinic acid (6.4) in a 1 000 ml volumetric flask. Dissolve and dilute to volume with
water (6.1).
The solution contains 5 147 mg/l of carbon and 1 000 mg/l of nitrogen.
The solution is stable for six months if stored at (3 ± 2) °C.
6.6 Blank solution.
Fill a 100 ml volumetric flask with water (6.1).
6.7 Gases or synthetic air, free from impurities with influence of the determinant (e.g. carbon dioxide,
organic carbon, nitrogen compounds).
Use gases in accordance with the manufacturer’s specifications, for example oxygen, 99,7 % volume
fraction.
4 © ISO 2018 – All rights reserved

ISO 20236:2018(E)
6.8 Reagents for the TOC or DOC determination.
6.8.1 Potassium hydrogen phthalate, C H KO .
8 5 4
6.8.2 Potassium hydrogen phthalate stock solution, ρ(C) = 1 000 mg/l.
Place 2,125 g of potassium hydrogen phthalate (6.8.1) in a 1 000 ml volumetric flask. Dissolve an
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