ISO 7725:2020

Rubber and rubber products - Determination of chlorine and bromine content

This document specifies methods for the determination of chlorine and/or bromine present in raw rubber as well as vulcanized or unvulcanized rubber compounds. The methods are applicable to natural rubbers and to the following synthetic rubbers: isoprene, styrene-butadiene, butadiene, butyl, halogenated butyl, nitrile, ethylene-propylene, chloroprene and epichlorohydrin.

Caoutchouc et produits à base de caoutchouc — Détermination de la teneur en brome et en chlore

General Information

• Status: Published
• Publication Date: 22-Jan-2020
• ICS: 83.060 - Rubber
• Technical Committee: ISO/TC 45/SC 2 - Testing and analysis
• Drafting Committee: ISO/TC 45/SC 2/WG 5 - Chemical tests
• Current Stage: 9093 - International Standard confirmed
• Start Date: 10-Jun-2025
• Completion Date: 13-Dec-2025

Relations

• Revises: ISO 7725:1991 - Rubber and rubber products - Determination of bromine and chlorine content - Oxygen flask combustion technique
• Effective Date: 10-Dec-2016

Overview

ISO 7725:2020 - Rubber and rubber products - Determination of chlorine and bromine content - specifies laboratory methods to quantify chlorine and bromine (halogen) content in raw, vulcanized and unvulcanized rubber. The standard covers natural rubber and common synthetic rubbers (isoprene, SBR, BR, butyl and halogenated butyl, nitrile, EPDM, chloroprene and epichlorohydrin). It defines sample-preparation routes and two analytical approaches: ion chromatography (IC) and potentiometric titration.

Key topics and technical requirements

• Scope and materials: Applies to raw rubber and rubber compounds; detects halogens present in polymer chains, additives or contaminants.
• Sample preparation (normative): Three combustion-based methods to convert sample to analysable solution:
  • Tubular furnace combustion (Annex A)
  • Oxygen combustion flask (Annex B)
  • Oxygen combustion bomb (Annex C) Two independent solutions per sample are required.
• Analytical methods:
  • Method A - Ion chromatography (Clause 6): Uses certified chloride/bromide standards, eluent and anion-exchange columns with conductivity detection (optionally with a suppressor). Preferred for very low halogen levels because of higher sensitivity.
  • Method B - Potentiometric titration (Clause 7): An established wet-chemistry titration route improved in this edition; suitable for routine determinations where titration end-points are well-defined.
• Calibration and calculation: Calibration curves from multiple standard concentrations are required. Results are calculated from sample and blank concentrations and reported as % mass of chlorine or bromine.
• Precision, reporting and safety: The standard specifies precision data (Clause 8) and test-report content (Clause 9). Warnings emphasize normal laboratory practice and environmental/safety handling of combustion and reagents. Hazardous reagents (e.g., mercury nitrate, hydrazine) have been removed from this edition.

Practical applications and typical users

• Quality control in rubber product manufacturing - verify halogen levels for performance and compatibility (e.g., flame-retardancy, vulcanization behavior).
• Incoming raw-material inspection for natural and synthetic rubber batches.
• Failure analysis and R&D - identify halogen-related degradation or contamination.
• Regulatory and environmental testing - monitor halogenated compound presence for compliance. Typical users: analytical laboratories, rubber compounders, OEMs, material scientists, and regulatory testing labs.

Related standards (referenced)

• ISO 1795 - Sampling of raw rubber
• ISO 4661-2 - Preparation of samples and test pieces for chemical tests
• ISO 3696 - Water for analytical laboratory use

Keywords: ISO 7725:2020, chlorine and bromine determination, rubber testing, halogen content, ion chromatography, potentiometric titration, sample combustion methods.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 7725
Second edition
2020-01
Rubber and rubber products —
Determination of chlorine and
bromine content
Caoutchouc et produits à base de caoutchouc — Détermination de la
teneur en brome et en chlore
Reference number
©
ISO 2020
© ISO 2020
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
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below or ISO’s member body in the country of the requester.
ISO copyright office
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Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Sample preparation . 2
5.1 Sampling . 2
5.2 Sample solutions . 2
6 Method A — Ion chromatography . 2
6.1 Reagents. 2
6.2 Apparatus . 3
6.3 Determination . 3
6.3.1 Setting up the ion chromatograph . 3
6.3.2 Preparation of the calibration curve . 3
6.3.3 Measuring blank solutions and sample solutions . 3
6.4 Calculation . 4
7 Method B — Potentiometric titration . 4
7.1 Reagents. 4
7.2 Apparatus . 5
7.3 Determination . 5
7.4 Calculation . 6
8 Precision . 7
9 Test report . 7
Annex A (normative) Preparation of sample solutions by the tubular furnace combustion
method . 8
Annex B (normative) Preparation of sample solutions by the oxygen combustion flask method .11
Annex C (normative) Preparation of sample solutions by the oxygen combustion bomb method .14
Annex D (informative) Conditions for ion chromatography .16
Annex E (informative) Precision results from an interlaboratory test programme .18
Bibliography .20
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
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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.
The committee responsible for this document is ISO/TC 45, Rubber and rubber products, Subcommittee
SC 2, Testing and analysis.
This second edition cancels and replaces the first edition (ISO 7725:1991), which has been technically
revised. The main changes compared to the previous edition are as follows:
— the ion chromatography method has been added in Clause 6;
— the titration procedure has been improved in Clause 7;
— the tubular furnace combustion method for sample preparation has been added in Annex A;
— the oxygen combustion flask method for sample preparation has been improved in Annex B;
— the oxygen combustion bomb method for sample preparation has been added in Annex C;
— mercury nitrate and hydrazine are no longer used due to their hazardous properties.
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 2020 – All rights reserved

Introduction
The two test methods in this document for quantitative analysis can be used for any type of rubbers
(i.e. raw rubber, vulcanized rubber or unvulcanized rubber) containing chlorine and/or bromine in any
form of existence, such as an element of polymer chain, chemical additives or a part of contaminations.
Three combustion methods are given for preparation of sample solution, i.e. tubular furnace
combustion method, oxygen combustion flask method and oxygen combustion bomb method. After
sample solutions are prepared, a content determination procedure, i.e. either ion chromatography or
potentiometric titration, follows. The most convenient and efficient method from the testing time and
safeness points of view, is the combination of tubular furnace combustion and ion chromatography, as
ion chromatography is widely used in quality control of polymer/rubber products or in environmental
analysis.
INTERNATIONAL STANDARD ISO 7725:2020(E)
Rubber and rubber products — Determination of chlorine
and bromine content
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
determine the applicability of any other restrictions.
WARNING 2 — Certain procedures specified in this document might 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 methods for the determination of chlorine and/or bromine present in raw
rubber as well as vulcanized or unvulcanized rubber compounds.
The methods are applicable to natural rubbers and to the following synthetic rubbers: isoprene,
styrene-butadiene, butadiene, butyl, halogenated butyl, nitrile, ethylene-propylene, chloroprene and
epichlorohydrin.
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 terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Principle
A sample solution is obtained by combustion of a test piece either burnt in a tubular furnace with
a stream of oxygen-containing gas and passed into a prepared solution or burnt in an oxygenic
atmosphere in a flask or a bomb which contains a solution to absorb the combustion gas. The sample
solution is then analysed by ion chromatography (method A) or potentiometric titration (method B) to
determine the content of chlorine and/or bromine in a sample.
For rubber samples of very low halogen content, method A is preferable since the inflection point might
not be obtained by method B.
5 Sample preparation
5.1 Sampling
For raw rubber, carry out sampling in accordance with ISO 1795.
For rubber compounds, carry out sampling in accordance with ISO 4661-2.
NOTE Chlorine and bromine contained in additives or contaminants can be detected by these sampling
methods, unless previously removed by extraction.
5.2 Sample solutions
To prepare sample solutions by the tubular furnace combustion method, follow the method specified in
Annex A. Repeat the procedure to create two solutions for each sample.
To prepare sample solutions by the oxygen combustion flask method, follow the method specified in
Annex B. Repeat the procedure to create two solutions for each sample.
To prepare sample solutions by the oxygen combustion bomb method, follow the method specified in
Annex C. Repeat the procedure to create two solutions for each sample.
If incomplete combustion, such as soot generation during combustion, is expected by the oxygen
combustion flask method, it is preferable to use the tubular furnace combustion method or the oxygen
combustion bomb method.
6 Method A — Ion chromatography
6.1 Reagents
6.1.1 Water, of grade 1 or higher. It shall be as specified in ISO 3696.
6.1.2 Chloride ion standard stock solution, of a commercial standard solution with a certified
chloride ion concentration, e.g. 1 000 mg/l of chloride, traceable to national standards. Comply with the
manufacturer’s expiration date or recommended shelf-life.
6.1.3 Chloride ion calibration solution, prepared by diluting the chloride ion standard stock solution
(6.1.2) with water (6.1.1). Prepare at least four solutions of different concentration of chloride ion covering
the expected concentration from the sample. The solutions shall be prepared every analytical day.
6.1.4 Bromide ion standard stock solution, of a commercial standard solution with a certified
bromide ion concentration, e.g. 1 000 mg/l of bromide, traceable to national standards. Comply with the
manufacturer’s expiration date or recommended shelf-life.
6.1.5 Bromide ion calibration solution, prepared by diluting the bromide ion standard stock solution
(6.1.4) with water (6.1.1). Prepare at least four solutions of different concentration of bromide ion covering
the expected concentration from the sample. The solutions shall be prepared every analytical day.
6.1.6 Mixed calibration solution, for measuring chloride ion and bromide ion at the same time,
prepared by mixing chloride ion (6.1.2) and bromide ion (6.1.4) with water (6.1.1). Prepare at least four
solutions of different concentration of chloride ion and bromide ion covering the expected concentration
from the sample. The solutions shall be prepared every analytical day.
6.1.7 Eluent solution, capable of eluting chloride ion and bromide ion to a proper retention time in
selected column. Follow the column manufacturer’s instructions.
2 © ISO 2020 – All rights reserved

NOTE Some examples of eluent are provided in Annex D.
6.2 Apparatus
6.2.1 Ion chromatograph, consisting of a pump to supply eluent, a sample injector, a column and a
conductivity detector specified as follows:
— pump: capable of delivering a constant flow within the range of 0,1 ml/min to 2,0 ml/min;
— sample injector: capable of injecting a constant volume of solution;
— column: filled with anion exchange resin suitable for resolving chloride ion and bromide ion from
other inorganic anions;
— suppressor: used for reducing the conductivity of high ionic eluent;
— detector: for detecting conductivity.
NOTE Some examples of commercially available column are provided in Annex D.
An ion chromatograph fitted with a suppressor as Figure 1 is suitable for sensitive analysis. The
suppressor is attached between a column and a detector.
An ion chromatograph without a suppressor as Figure 2 may also be selected.
Figure 1 — Example of basic ion chromatography system with suppressor
Figure 2 — Example of basic ion chromatography system without suppressor
6.3 Determination
6.3.1 Setting up the ion chromatograph
Set up the ion chromatograph in accordance with the manufacturer’s instructions.
6.3.2 Preparation of the calibration curve
Inject the calibration solutions in increasing order of concentration and measure the conductivity of
chloride ion and bromide ion 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.
6.3.3 Measuring blank solutions and sample solutions
Inject the blank solution and sample solutions (created in 5.2) to measure the peak areas in sequence.
Then determine the chloride ion and bromide ion concentration of the blank (C and C , respectively)
B1 B2
as well as the concentration of the individual sample solution (C and C , respectively) by using the
S1 S2
calibration curve determined in 6.3.2.
6.4 Calculation
Calculate the chlorine content (w ) and/or bromine content (w ), in percentage by mass, by
1 2
Formulae (1) and (2), using the two determination values in 6.3. Average the results and round to the
second decimal place.
CC− ×V
()
SB11
w = ×100 (1)
W×1000
CC− ×V
()
SB22
w = ×100 (2)
W×1000
where
W is the mass of the test piece, in mg (see A.4.2, B.4.1 or C.4.1);
C is the chloride ion concentration of the sample solution, in mg/l;
S1
C is the chloride ion concentration of the blank solution, in mg/l;
B1
C is the bromide ion concentration of the sample solution, in mg/l;
S2
C is the bromide ion concentration of the blank solution, in mg/l;
B2
V is the fixed amount of the solution, in ml (see A.4.5, B.4.9 or C.4.8).
7 Method B — Potentiometric titration
7.1 Reagents
7.1.1 Water, of grade 1 or higher. It shall be as specified in ISO 3696.
7.1.2 Nitric acid, concentrated, ρ = 1,42 g/cm .
7.1.3 0,5mol/l Nitric acid, c(HNO ) = 0,5 mol/l, obtained by diluting 30 ml of concentrated nitric acid
(7.1.2) to 1 000 ml with water (7.1.1).
NOTE Commercially available 0,5 mol/l nitric acid can be used.
7.1.4 Silver nitrate standard volumetric solution, c(AgNO ) = 0,02 mol/l.
Standardize a silver nitrate solution obtained by dissolving 3,4 g of silver nitrate in 1 000 ml of water
(7.1.1) as follows:
Take a measured volume (between 1 ml and 5 ml) of sodium chloride solution (7.1.5), dilute with water
(7.1.1) to 25 ml in a 50 ml beaker, and add 2 ml of 0,5 mol/l nitric acid (7.1.3) along with a stirring
bar. Place the solution on a stirrer (7.2.2) and titrate with the silver nitrate solution (7.1.4) using an
automatic titrator (7.2.3). Read the volume from the automatic titrator. Determine the factor ( f) from
the averaged result in duplicating the same procedure.
Commercially available 0,02 mol/l silver nitrate standard volumetric solution and its guaranteed
factor ( f ) can be used.
7.1.5 Sodium chloride solution, traceable to national standards. c(NaCl) = 0,02 mol/l.
Alternatively, dissolve 1,168 g of sodium chloride in 1 000 ml of water (7.1.1).
4 © ISO 2020 – All rights reserved

7.1.6 Aluminium nitrate, of analytical reagent grade.
NOTE Aluminium nitrate is used to minimize the mutual interference caused by co-precipitation of chloride
and bromide.
7.1.7 Ethanol, of analytical reagent grade.
Alternatively, 2-propanol may be substituted wherever ethanol is specified.
7.2 Apparatus
7.2.1 Electronic balance, capable of weighing to the nearest 0,01 mg.
7.2.2 Magnetic stirrer and a stirring bar.
7.2.3 Automatic titrator.
7.2.4 Silver electrode, to be used as a measuring electrode.
7.2.5 Reference electrode, of the salt bridge type.
NOTE It is possible to use a combined electrode instead of the silver electrode and the reference electrode.
7.3 Determination
7.3.1 Transfer the blank solutions and sample solutions (created in 5.2) obtained quantitatively to a
300 ml beaker each with several washes water. Place a magnetic stirring bar in the beaker and place the
assembly on the magnetic stirrer (7.2.2).
7.3.2 Add 2 ml of the 0,5 mol/l nitric acid (7.1.3) and 2 g of the aluminium nitrate (7.1.6). Continue
stirring to dissolve the aluminium nitrate, then add 160 ml of ethanol (7.1.7).
7.3.3 Insert the electrode pair (7.2.4 and 7.2.5) into the solution and titrate with the silver nitrate
solution (7.1.4) with an automatic titrator (7.2.3).
NOTE The problem is least when bromine is in excess. At its worst, when chlorine is in excess, the bromine
concentration might appear high, to an extent of 5 % of the chloride ion content. The problem can be minimized
[2]
by carrying out the titrat
...