IEC 60746-2:2003

INTERNATIONAL IEC
STANDARD
60746-2
Second edition
2003-01
Expression of performance of
electrochemical analyzers –
Part 2:
pH value
Expression des qualités de fonctionnement
des analyseurs électrochimiques –
Partie 2:
Mesure du pH
Reference number
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INTERNATIONAL IEC
STANDARD
60746-2
Second edition
2003-01
Expression of performance of
electrochemical analyzers –
Part 2:
pH value
Expression des qualités de fonctionnement
des analyseurs électrochimiques –
Partie 2:
Mesure du pH
 IEC 2003  Copyright - all rights reserved
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mechanical, including photocopying and microfilm, without permission in writing from the publisher.
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– 2 – 60746-2  IEC:2003(E)
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative reference . 6
3 Definitions . 6
4 Procedure for specification . 8
4.1 Additional statements on sensor units and analyzers. . 9
4.2 Additional statements on electronic units . 9
4.3 Statements on sensors .10
4.3.1 General.10
4.3.2 Reference electrodes.10
4.3.3 pH sensor .10
4.3.4 Temperature compensator .10
4.3.5 Auxiliary devices for sensor unit.10
5 Recommended standard values and ranges of influence quantities affecting the
performance of electronic units .11
6 Verification of values .11
6.1 General aspects .11
6.2 Test procedures for electronic units .11
6.2.1 pH scaling.11
6.2.2 Isopotential pH, pH .12
i
6.2.3 Temperature compensation.12
6.3 Test procedures for sensor units.12
6.3.1 Zero point pH.12
6.3.2 Percentage theoretical slope, PTS .12
6.3.3 Isopotential pH , pH .12
i
6.4 Test procedures for analyzers.12
6.4.1 Intrinsic uncertainty.13
6.4.2 Linearity uncertainty.13
6.4.3 Repeatability.13
6.4.4 Output fluctuation .13
6.4.5 Warm-up time .13
6.4.6 Drift .13
6.4.7 Response times .13
6.4.8 Sample temperature.13
6.4.9 Primary influence quantities.13
Bibliography.21
Annex A (informative).15
Annex B (informative) Reference buffer solutions: pH as a function of temperature .16
Annex C (normative) Alternative procedures for measuring response times: delay
(T ), rise (fall) (T T ) and 90% (T ) times .19
10 r , f 90
60746-2  IEC:2003(E) – 3 –
Figure C.1 – Relation between T , T (T ) and T .19
10 r f 90
Table A.1 – Values of the slope factor, k = 2,3026 R.T/F.15
Table B.1 – Values of reference pH buffer solutions at various temperatures .17
Table B.2 – Composition of reference pH buffer solutions .18

– 4 – 60746-2  IEC:2003(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
EXPRESSION OF PERFORMANCE OF
ELECTROCHEMICAL ANALYZERS –
Part 2: pH value
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International
Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60746-2 has been prepared by subcommittee 65D: Analysing
equipment, of IEC technical committee 65: Industrial-process measurement and control.
This second edition cancels and replaces the first edition published in 1982 and constitutes a
technical revision.
The text of this standard is based on the following documents:
FDIS Report on voting
65D/90A/FDIS 65D/94/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
The contents of this second edition remain substantially unchanged.
The major change is that Annex B has been updated in line with recent IUPAC
Recommendations for the measurement of pH.
This part of IEC 60746 shall be used in conjunction with IEC 60746-1, which includes further
definition of the scope and provides for the general aspects of all electrochemical analyzers.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

60746-2  IEC:2003(E) – 5 –
The committee has decided that the contents of this publication will remain unchanged
until 2007. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of May 2003 and July 2003 have been included in this
copy.
– 6 – 60746-2  IEC:2003(E)
EXPRESSION OF PERFORMANCE OF
ELECTROCHEMICAL ANALYZERS –
Part 2: pH value
1 Scope
This International Standard is intended:
– to specify terminology, definitions and requirements for statements by manufacturers for
analyzers, sensor units and electronic units used for the determination of the pH of
aqueous solutions;
– to establish performance tests for such analyzers, sensor units and electronic units;
– to provide basic documents to support the applications of quality assurance standards ISO
9001, ISO 9002 and ISO 9003.
2 Normative reference
The following referenced documents are indispensable for the application 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.
IEC 60746-1:2002, Expression of performance of electrochemical analyzers – Part 1: General
ISO 9001, Quality management systems – Requirements
ISO 9002, Quality systems – Model for quality assurance in production, installation and
servicing
ISO 9003, Quality systems – Model for quality assurance in final inspection and test
3 Terms, definitions, symbols and abbreviations
3.1 Terms and definitions
For the purposes of this part of IEC 60746, the definitions given in Clause 3 of IEC 60746-1,
as well as the following apply.
3.1.1
pH value
A measure of the conventional hydrogen ion activity a (see equation (1)), in an aqueous
H+
solution given by the expression:
pH = –log a
H+
It is measured with respect to pH values assigned to certain reference pH buffer solutions.
The measurement is performed by determining the e.m.f., E, between a pair of electrodes
immersed in the sample to be measured, according to the cell scheme:
Reference electrode I Sample I pH electrode E
and a measurement with the same electrode pair at the same temperature in a reference
buffer solution of pH (S ) according to
60746-2  IEC:2003(E) – 7 –
Reference electrode I Buffer (S ) I pH electrode E(S )
1 1
The e.m.f.s E(S ), etc. are defined as the difference of the potential of the right-hand (pH)
electrode minus the potential of the left-hand (reference) electrode.
The pH of the sample is then given ideally by:
E − E(S )
pH = pH(S ) − (1)
k
where k = 2,3026 R.T/F, the theoretical, Nernstian, slope (see 3.1.2) .
Numerical values for k, the theoretical slope factor, at temperatures from 0 °C to 95 °C, are
given in Annex A.
NOTE Measurements in non or partially aqueous media are beyond the scope of this document; the reader should
refer to specialist texts.
3.1.2
practical slope factor and percentage theoretical slope
PTS
performance of the electrode pair may fall below the theoretical slope k exhibiting the practical
slope k′ which m
...