IEC TR 62434:2006

TECHNICAL IEC
REPORT TR 62434
First edition
2006-03
pH measurements in difficult media –
Definitions, standards and procedures

Reference number
IEC/TR 62434:2006(E)
Publication numbering
As from 1 January 1997 all IEC publications are issued with a designation in the
60000 series. For example, IEC 34-1 is now referred to as IEC 60034-1.
Consolidated editions
The IEC is now publishing consolidated versions of its publications. For example,
edition numbers 1.0, 1.1 and 1.2 refer, respectively, to the base publication, the
base publication incorporating amendment 1 and the base publication incorporating
amendments 1 and 2.
Further information on IEC publications
The technical content of IEC publications is kept under constant review by the IEC,
thus ensuring that the content reflects current technology. Information relating to
this publication, including its validity, is available in the IEC Catalogue of
publications (see below) in addition to new editions, amendments and corrigenda.
Information on the subjects under consideration and work in progress undertaken
by the technical committee which has prepared this publication, as well as the list
of publications issued, is also available from the following:
• IEC Web Site (www.iec.ch)
• Catalogue of IEC publications
The on-line catalogue on the IEC web site (www.iec.ch/searchpub) enables you to
search by a variety of criteria including text searches, technical committees
and date of publication. On-line information is also available on recently issued
publications, withdrawn and replaced publications, as well as corrigenda.
• IEC Just Published
This summary of recently issued publications (www.iec.ch/online_news/ justpub)
is also available by email. Please contact the Customer Service Centre (see
below) for further information.
• Customer Service Centre
If you have any questions regarding this publication or need further assistance,
please contact the Customer Service Centre:

Email: custserv@iec.ch
Tel: +41 22 919 02 11
Fax: +41 22 919 03 00
TECHNICAL IEC
REPORT TR 62434
First edition
2006-03
pH measurements in difficult media –
Definitions, standards and procedures

 IEC 2006  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale U

International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue

– 2 – TR 62434  IEC:2006(E)
CONTENTS
FOREWORD.3

1 Scope and object.5
2 Normative references .5
3 General principles .5
3.1 Terms and definitions .5
3.2 Symbols .5
3.3 pH value.5
3.4 Standard reference buffer solutions (primary and secondary pH standards) .7
3.5 Widths of normal pH scales or normal pH ranges in the general solvents Z .10
3.6 Electrodes and operating conditions .12
4 Solvent media of applicability .14
5 Procedure for specification .14
6 Recommended standard values and ranges of influence quantities .14
7 Verification of values .14
8 Other difficult media for pH determinations .15

Annex A (informative) Values of the Nernstian slope factor k = 2,3026 RT/F.16
Annex B (informative) .17
Annex C (informative) .22
Annex D (informative) .23
Annex E (informative) .26
Annex F (informative) .27

Bibliography.28

Figure 1 – Schematic structure of the hydrogen gas electrode and of the AgCl
electrode forming the cell (13) .9
Figure 2 – Intercomparing widths and relative positions of normal pH scales
(with neutral points indicated by halving dots) in different solvents .11

Table A.1 – Values of the Nernstian slope factor k = 2,3026 RT/F.16

TR 62434  IEC:2006(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
pH MEASUREMENTS IN DIFFICULT MEDIA –
DEFINITIONS, STANDARDS AND PROCEDURES

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of 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, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). 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. 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 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 IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC 62434, which is a technical report, has been prepared by subcommittee 65D: Analyzing
equipment, of IEC technical committee 65: Industrial-process measurement and control.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
65D/121/DTR 65D/124/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 4 – TR 62434  IEC:2006(E)
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this Technical report may be issued at a later date.

TR 62434  IEC:2006(E) – 5 –
pH MEASUREMENTS IN DIFFICULT MEDIA –
DEFINITIONS, STANDARDS AND PROCEDURES

1 Scope and object
This Technical Report concerns analyzers, sensor units and electronic units used for the
determination of pH in non-aqueous solvents and aqueous organic solvent mixtures using
glass electrodes. IEC 60746-1 includes further definition of the scope and provides for the
general aspects of all electrochemical analyzers, including pH. It is worthwhile to remind that
IEC 60746-2 contains specifications for simulators used for testing pH electronic units.
This technical report specifies the terminology, definitions, methodology, requirements for
statements by manufacturers and performance tests for analyzers, sensor units and electronic
units used for the determination of pH value in non-aqueous and aqueous-organic solvent
mixtures.
2 Normative references
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, Expression of performance of electrochemical analyzers – Part 1: General
IEC 60746-2, Expression of performance of electrochemical analyzers – Part 2: pH value
3 General principles
3.1 Terms and definitions
The required definitions will be given following on the order of appearance of the relevant
physical quantities in the text, and they comply with the pertinent IUPAC documents [1,2]
and IEC 60746-2.
3.2 Symbols
The meaning of each symbol used here is given immediately after its first appearance in the
relevant equation and it is conform to the pertinent IUPAC documents [1,2] and
IEC 60746-2.
3.3 pH value
3.3.1 General
A measure of the conventional hydrogen ion activity a in solution given by the expression
H+
pH = −log a = −log(m γ) (1)
H+ H+ H+
+ +
where γ is the activity coefficient of the H ion at the molality m (moles of H per kg of
H+ H+
solvent). pH is a dimensionless quantity; it is not correct to write the logarithm of a quantity
other than a dimensionless number, and the full form of equation (1) is
———————
Numbers in square brackets refer to the bibliography.

– 6 – TR 62434  IEC:2006(E)
pH = −log a = −log(m γ /m°) (2)
H+ H+ H+
−1
where m° = 1 mol kg is the standard-state reference molality. This definition is in terms of
the molal scale, which is that recommended by IUPAC for a key reason, i.e. the molality of a
solution is temperature-independent, which saves much repetitive work of cell construction
and filling. However, if one wants to treat pH in terms of the amount-of-substance
−3
concentration c (formerly “molarity”) in mol dm , the equation (2) would take the form
pH = −log(a ) = −log(c y /c°) (3)
c H+ c H+ H+
+ + 3
where y is the activity coefficient of H at concentration c (moles of H per dm of
H+ H+
solvent). It is worthwhile to recall that pH and pH are interrelated by the equation
c
−3
pH = pH − log [ρ/(kg dm)] (4)
c
where ρ is the relative density of the solvent.
Although equation (2), or alternatively (4), can be used to give an interpretation to pH values
under certain limiting conditions, a cannot be rigorously obtained by any method, for
H+
example from potential difference measurements, because it involves such a non-
+
thermodynamic quantity as the single-H -ion activity coefficient y , and instead an
H+
operational definition is adopted in terms of pH values assigned to certain reference buffers
(primary or secondary pH standards). The pH measurement is performed by measuring the
potential difference (electromotive force) E between a pair of electrodes immersed in the
X
sample at unknown pH in the (non-aqueous or aqueous-organic) solvent Z, according to the
X
cell scheme:
+
Reference C
...