IEC TR 62434:2006

pH measurements in difficult media - Definitions, standards and procedures

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.

General Information

• Status: Published
• Publication Date: 12-Mar-2006
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 19.080 - Electrical and electronic testing
• ICS: 71.040.40 - Chemical analysis
• Technical Committee: SC 65B - Measurement and control devices
• Drafting Committee: WG 14 - TC 65/SC 65B/WG 14
• Current Stage: PPUB - Publication issued
• Start Date: 15-Mar-2006
• Completion Date: 13-Mar-2006

Standards Content (Sample)

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)
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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
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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
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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
...