ISO 26603:2026

International
Standard
ISO 26603
Third edition
Plastics — Aromatic isocyanates
2026-04
for use in the production of
polyurethanes — Determination of
total chlorine
Plastiques — Isocyanates aromatiques destinés à la production
de polyuréthanes — Dosage du chlore total
Reference number
© ISO 2026
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
4.1 General .2
4.2 Test Method A .2
4.3 Test Method B .2
4.4 Test Method C .2
5 Interferences . 2
6 Sampling . 2
7 Test Method A — Total chlorine by oxygen bomb . 3
7.1 Reagents .3
7.2 Apparatus .3
7.3 Procedure .4
7.4 Calculation .5
7.5 Precision and bias .6
7.5.1 General .6
7.5.2 Precision .6
7.5.3 Bias .6
8 Test Method B — Total chlorine by Schöniger oxygen flask . 6
8.1 Reagents .6
8.2 Apparatus .6
8.3 Procedure .7
8.4 Calculation .7
8.5 Precision and bias .7
8.5.1 General .7
8.5.2 Precision .8
8.5.3 Bias .8
9 Test Method C — Total chlorine by microcoulometry . 8
9.1 Reagents .8
9.2 Apparatus .9
9.3 Procedure .9
9.4 Calculation .10
9.5 Precision and bias .10
9.5.1 General .10
9.5.2 Precision .10
9.5.3 Bias .11
10 Test report .11
Bibliography .12

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,
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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 document 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)
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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 61, Plastics, Subcommittee SC 12, Thermosetting
materials.
This third edition cancels and replaces the second edition (ISO 26603:2017), which has been technically
revised.
The main changes are as follows:
— Test Method C has been added:
— in Clause 4, a new subclause 4.4 has been added;
— a new Clause 9 has been added and subsequent clauses have been renumbered.
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
Introduction
Isocyanates are typically produced by phosgenation of an aromatic amine using chlorine-substituted
benzenes (e.g. o-dichlorobenzene) as reaction solvents. ISO 15028 is used to determine the hydrolyzable
chlorine content of the isocyanates. The test methods in this document are used to determine the total
chlorine content of aromatic isocyanates. The difference between the total chlorine content and the
hydrolyzable chlorine content is a measure of the reaction solvents left in the product, and therefore is a
useful tool for assessing product quality.
NOTE This document is technically equivalent to ASTM D4661–03.

v
International Standard ISO 26603:2026(en)
Plastics — Aromatic isocyanates for use in the production of
polyurethanes — Determination of total chlorine
SAFETY PRECAUTIONS — Persons using this document should be familiar with normal laboratory
practice, if applicable. This document does not purport to address all of the safety concerns, if any,
associated with its use. It is the responsibility of the user of this document to establish appropriate
safety and health practices, and to determine any regulatory requirements before use.
1 Scope
This document specifies the determination of the total chlorine content of aromatic isocyanates used in the
preparation of polyurethanes.
The difference between the total chlorine content and the hydrolyzable chlorine content (see ISO 15028) is a
measure of the process solvents left in the product. All the test methods are applicable to a variety of organic
compounds, including aliphatic isocyanates, but the amount of sample used might need to be adjusted.
These test methods can be used for research or for quality control.
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 1042, Laboratory glassware — One-mark volumetric flasks
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 6353-2, Reagents for chemical analysis — Part 2: Specifications — First series
ISO 6353-3, Reagents for chemical analysis — Part 3: Specifications — Second series
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
isocyanate
organic compound containing one or more NCO groups
3.2
polyurethane
polymer prepared by the reaction of an organic di- or polyisocyanate with compounds containing two or
more hydroxyl groups
3.3
hydrolyzable chlorine
organic or inorganic chlorine compounds formed in the production of isocyanates that react with methanol
under the conditions of ISO 15028 to liberate hydrogen chloride
3.4
total chlorine
inorganic and organically bound chlorine present in isocyanates that is converted to titratable chlorides
under the combustion conditions of the test
4 Principle
4.1 General
In test methods A and B, the organic matter in the sample is destroyed by combustion with oxygen, thus
converting the organically combined chlorine to ionic chloride. The chloride is determined potentiometrically
by titration with silver nitrate (AgNO ) solution.
4.2 Test Method A
Combustion of the sample is done in a pressurized oxygen bomb.
4.3 Test Method B
Combustion is done at atmospheric pressure in a Schöniger oxygen flask.
NOTE For information on the Schöniger flask, see Reference [6].
4.4 Test Method C
Organic chlorine compounds are converted into hydrogen chloride through a pyrolysis furnace.
+ -
Hydrogen chloride dissolves in the electrolyte and dissociates into hydrogen and chloride ions (H , Cl ) in the
Titration Cell. The chloride ions react with silver ions created via electrolysis to form silver chloride (AgCl)
The end point of titration is displayed by potentiometry. In accordance with Faraday's law, the amount of
chloride ions can be calculated based on the amount of charge consumed to produce silver ions.
5 Interferences
Thiocyanate, cyanide, sulphide, bromide, iodide or other substances capable of reacting with silver ion, as
well as substances capable of reducing silver ion in acid solution, interferes with the determination.
6 Sampling
Since organic isocyanates react with atmospheric moisture, take special precautions in sampling. Usual
sampling methods, even when conducted rapidly, can expose the isocyanate to moisture and cause
contamination of the sample with insoluble ureas; therefore, blanket the sample with a dry inert gas (e.g.
nitrogen, argon or dried air) at all times.
WARNING — Organic isocyanates are hazardous when absorbed through the skin, or when the
vapours are breathed.
CAUTION — Provide adequate ventilation and wear protective gloves and eyeglasses.

7 Test Method A — Total chlorine by oxygen bomb
7.1 Reagents
7.1.1 Purity of reagents
Reagent-grade chemicals shall be used in all tests. Other grades may be used, provided that it is first
determined that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of
the determination. Unless otherwise indicated, all reagents shall conform to the specifications of ISO 6353-2
and ISO 6353-3.
7.1.2 Purity of water
Unless otherwise indicated, references to water shall be understood to mean grade 2 water as defined by
ISO 3696.
7.1.3 Ethyl alcohol, conforming to ISO 6353-2.
7.1.4 Nitric acid (diluted). While stirring vigorously, add 100 ml of nitric acid (HNO , specific gravity
1,42) to 100 ml of water cooled in an ice bath.
7.1.5 Oxygen, free of combustible materials and halogen compounds.
7.1.6 Silver nitrate, standard solution (0,01 M). Prepare a 0,01 M silver nitrate (AgNO ) solution and
check frequently enough to detect changes of 0,000 5 M, either gravimetrically or potentiometrically, using
standard hydrochloric acid (HCl).
7.1.7 Sodium carbonate solution (50 g/l). Dissolve 135 g of sodium carbonate decahydrate
(Na CO ·10H O) in water and dilute to 1 l.
2 3 2
7.2 Apparatus
7.2.1 Weighing bottle and balance, suitable for weighing a liquid sample by difference to the nearest
0,5 mg.
7.2.2 Oxygen bomb apparatus. A corrosion-resistant steel reactor capable of being pressurized to 40
atmospheres of pure oxygen, followed by electrical ignition of the sample by use of an internal fuse wire. The
bomb shall be capable of withstanding the pressure build-up caused by the combustion of the sample. Parr
Bomb No. 1108 is a suitable device (see Figure 1). Equivalent apparatus may be substituted with appropriate
changes in the procedure.
7.2.3 Fuse wire, iron-nickel-chromium, No. 34 B and S gage.
7.2.4 Titrimeter, automatic (preferred) or manual, equipped with a silver/silver chloride electrode pair
and a 10 ml capacity m
...