ISO 19242:2021

INTERNATIONAL ISO
STANDARD 19242
Second edition
2021-10
Rubber — Determination of total
sulfur content by ion chromatography
Caoutchouc — Détermination de la teneur en soufre total par
chromatographie ionique
Reference number
© ISO 2021
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
4.1 Combustion . 2
4.1.1 Tubular furnace combustion method . 2
4.1.2 Oxygen combustion flask method . 2
4.2 Determination . 2
5 Reagents . 2
6 Apparatus . 2
7 Procedure .3
7.1 Preparation of sample solutions . 3
7.1.1 Tubular furnace combustion method . 3
7.1.2 Oxygen combustion flask method . 3
7.2 Determination of sulfate by ion chromatography. 3
7.2.1 Setting up the ion chromatograph . 3
7.2.2 Measuring calibration solutions . 3
7.2.3 Measuring blank solutions and sample solutions . 4
8 Calculations . 4
9 Precision . 4
10 Test report . 4
Annex A (normative) Preparation of sample solutions by the tubular furnace combustion
method . 5
Annex B (normative) Preparation of sample solutions by the oxygen combustion flask
method . 8
Annex C (informative) Examples of conditions for ion chromatography .11
Annex D (informative) Precision data from an interlaboratory test programme .13
Bibliography .15
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).
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 45, Rubber and rubber products,
Subcommittee SC 2, Testing and analysis.
This second edition cancels and replaces the first edition (ISO 19242:2015), of which it constitutes a
minor revision. The main changes compared to the previous edition are as follows:
— the CAS numbers have been added for all chemicals listed in this document;
— Clause 3 on “Terms and definitions” has been added.
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
Titration methods using thorin, a toxic arsenic compound as a reagent, have been used to determine the
total sulfur content in raw rubber and rubber compounds. In this document, the sulfur in a test piece
is burnt and oxidized to sulfur dioxide, which is then absorbed into a hydrogen peroxide solution and
converted to sulfuric acid for determination by ion chromatography.
No hazardous reagents are required, thus improving the working environment as well as being eco-
friendly. In addition, ion chromatography is used worldwide for its simplicity and high accuracy.
v
INTERNATIONAL STANDARD ISO 19242:2021(E)
Rubber — Determination of total sulfur content by ion
chromatography
WARNING 1 — 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 and to
ensure compliance with any national regulatory conditions.
WARNING 2 — The use of this document pre-supposes sufficient working knowledge of the
principles and techniques of ion chromatography for the analyst to perform the operations
described and interpret the results correctly.
CAUTION — Certain procedures specified in this document can involve the use or generation
of substances, or the generation of waste, that could constitute a local environmental hazard.
Reference should be made to appropriate documentation on safe handling and disposal after
use.
1 Scope
This document specifies a method for the determination of the total sulfur content of raw rubber and
unvulcanized or vulcanized rubber compounds by ion chromatography following the preparation of a
sample solution using either a tubular furnace combustion or an oxygen combustion flask method.
The tubular furnace combustion method is applicable for rubbers with sulfur content less than 0,1 % as
it is possible that the oxygen combustion flask method will not give sufficiently accurate results.
The oxygen combustion flask method is not applicable to rubbers containing a metal salt that forms an
insoluble metal sulfate, such as barium sulfate (CAS 7727-43-7).
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 1795, Rubber, raw natural and raw synthetic — Sampling and further preparative procedures
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4661-2, Rubber, vulcanized — Preparation of samples and test pieces — Part 2: Chemical tests
3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Principle
4.1 Combustion
4.1.1 Tubular furnace combustion method
A test piece is burnt in an oxygen (CAS 7782-44-7) stream in a tubular furnace with an electrical
heater. The sulfur in the test piece is oxidized to sulfur dioxide (CAS 7446-09-5), which is absorbed into
hydrogen peroxide (CAS 7722-84-1) solution and converted to sulfuric acid (CAS 7664-93-9).
4.1.2 Oxygen combustion flask method
A test piece is burnt in the presence of oxygen in a flask. The sulfur in the test piece is oxidized to sulfur
dioxide, which is absorbed into hydrogen peroxide solution and converted to sulfuric acid.
4.2 Determination
The sulfate from either the tubular furnace combustion or the oxygen combustion flask method is
quantitatively analysed by ion chromatography, and the result is converted to the total sulfur content of
the original rubber sample.
5 Reagents
Use only reagents of recognized analytical grade and only water as specified in 5.1. The reagents for
the tubular furnace combustion method are given in A.2. The reagents for the oxygen combustion flask
method are given in B.2.
5.1 Water, of grade 1 or higher as specified in ISO 3696.
5.2 Sulfate stock standard solution, of a commercial standard solution with a certified sulfate
concentration, e.g. 1 000 mg/dm of sulfate, traceable to national standards.
Observe the manufacturer's expiry date or recommended shelf-life.
5.3 Sulfate calibration solutions, prepared by dilution of the sulfate stock standard solution (5.2)
with water (5.1).
Prepare at least four solutions of different concentration of sulfate covering the expected concentration
from the sample. The solutions shall be prepared every analytical day.
5.4 Eluent solution, capable of eluting sulfate to a proper retention time in selected column.
Follow the column manufacturer’s instructions. Some examples of eluent are shown in Annex C.
6 Apparatus
6.1 Balance, of accuracy to the nearest 0,1 mg.
6.2 Apparatus for the tubular furnace combustion method, as specified in A.3.
6.3 Apparatus for the oxygen combustion flask method, as specified in B.3.
6.4 Ion chromatograph, consisting of a pump to supply eluent, injection valve, column and
conductivity detector specified as follows:
3 3
— pump: capable of delivering a constant flow within the range of 0,1 cm /min to 2,0 cm /min;
— injection valve: capable of injecting a constant volume of solution;
— column: filled with anion exchange resin suitable for resolving sulfates from other inorganic anions;
some examples are shown in Annex C;
— suppressor: used for reducing the conductivity of high ionic eluent;
— detector: for detecting conductivity.
An ion chromatograph fitted with a suppressor is suitable for sensitive analysis (see Figure 1). The
suppressor is attached between the column and the detector. However, an ion chromatograph without a
suppressor may also be selected (see Figure 2). For the conditions of these methods, see Annex C.

Figure 1 — Example of basic ion chromatography system with suppressor
Figure 2 — Example of basic ion chromatography system without suppressor
7 Procedure
7.1 Preparation of sample solutions
7.1.1 Tubular furnace combustion method
Follow the method specified in Annex A. Repeat the procedure to obtain two solutions for each sample.
7.1.2 Oxygen combustion flask method
Follow the method specified in Annex B. Repeat the procedure to obtain two solutions for each sample.
7.2 Determination of sulfate by ion chromatography
7.2.1 Setting up the ion chromatograph
Set up the ion chromatograph in accordance with the manufacturer’s instructions.
7.2.2 Measuring calibration solutions
Inject the calibration solutions in order of increasing concentration and measure the conductivity of
sulfate peak area in each solution. Determine the correlation formula (calibration curve) by plotting the
peak area as a function of concentration by means of linear regression.
7.2.3 Measuring blank solutions and sample solutions
Inject the blank soluti
...