IEC TR 62434-2006 pH measurements in difficult media - Definitions standards and procedures《难选介质的pH值测量.定义、标准和程序》.pdf

《IEC TR 62434-2006 pH measurements in difficult media - Definitions standards and procedures《难选介质的pH值测量.定义、标准和程序》.pdf》由会员分享，可在线阅读，更多相关《IEC TR 62434-2006 pH measurements in difficult media - Definitions standards and procedures《难选介质的pH值测量.定义、标准和程序》.pdf（34页珍藏版）》请在麦多课文档分享上搜索。

1、 TECHNICAL REPORT IEC TR 62434First edition 2006-03pH 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

2、 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 incorpora

3、ting 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 C

4、atalogue 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 f

5、rom 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 r

6、ecently issued publications, withdrawn and replaced publications, as well as corrigenda.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. Custo

7、mer Service Centre If you have any questions regarding this publication or need further assistance, please contact the Customer Service Centre: Email: custserviec.ch Tel: +41 22 919 02 11 Fax: +41 22 919 03 00 TECHNICAL REPORT IEC TR 62434First edition 2006-03pH measurements in difficult media Defin

8、itions, standards and procedures PRICE CODE 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

9、Electrotechnical Commission, 3, rue de Varemb, PO Box 131, CH-1211 Geneva 20, Switzerland Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmailiec.ch Web: www.iec.ch U For price, see current catalogue Commission Electrotechnique Internationale International Electrotechnical Commission

10、 2 TR 62434 IEC:2006(E) CONTENTS FOREWORD.3 1 Scope and object5 2 Normative references .5 3 General principles 5 3.1 Terms and definitions 5 3.2 Symbols 5 3.3 pH value5 3.4 Standard reference buffer solutions (primary and secondary pH standards) 7 3.5 Widths of normal pH scales or normal pH ranges i

11、n the general solvents Z .10 3.6 Electrodes and operating conditions12 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 (info

12、rmative) 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 Bibliography28 Figure 1 Schematic structure of the hydrogen gas electrode and of the AgCl electrode formi

13、ng 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 _

14、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 inte

15、rnational 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 (hereaft

16、er 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 partic

17、ipate 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

18、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 r

19、easonable 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

20、 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

21、 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 individ

22、ual 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, th

23、is 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 th

24、is 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 w

25、hen 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 meas

26、urement 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 publicat

27、ion 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 th

28、e 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

29、 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 aspe

30、cts 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 per

31、formance 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

32、 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

33、 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 1,21and IEC 60746-2. 3.2 Symbols The meaning of each symbol used here is given

34、 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 H+in solution given by the expression pH = log a H+= log(m H+ H+ ) (1) where H+is

35、the activity coefficient of the H +ion at the molality m H+(moles of H +per kg of 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 1Numbers in square brackets refer to the bibliogr

36、aphy. 6 TR 62434 IEC:2006(E) pH = log a H+= log(m H+ H+ /m) (2) where m = 1 mol kg 1is 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 m

37、uch repetitive work of cell construction and filling. However, if one wants to treat pH in terms of the amount-of-substance concentration c (formerly “molarity”) in mol dm 3 , the equation (2) would take the form pH c= log(a H+ ) c= log(c H+y H+ /c) (3) where y H+is the activity coefficient of H +at

38、 concentration c H+(moles of H +per dm 3of solvent). It is worthwhile to recall that pH and pH care interrelated by the equation pH c= pH log /(kg dm 3 ) (4) where is the relative density of the solvent. Although equation (2), or alternatively (4), can be used to give an interpretation to pH values

39、under certain limiting conditions, a H+cannot be rigorously obtained by any method, for example from potential difference measurements, because it involves such a non- thermodynamic quantity as the single-H + -ion activity coefficient y H+ , and instead an operational definition is adopted in terms

40、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 Xbetween a pair of electrodes immersed in the sample at unknown pH Xin the (non-aqueous or aqueous-organic) solvent Z,

41、 according to the cell scheme: Reference electrode in solvent Z Concentrated equitransferent salt bridge in solvent Z Sample at unknown pH Xin solvent Z H + sensing electrode (hydrogen gas electrode, or glass electrode) (5) and measuring the potential difference E Swith the same electrode pair, the

42、same salt bridge of the same composition and solvent Z, and at the same temperature, in a reference buffer solution of known standard pH PSor pH SS , according to: Reference electrode in solvent Z Concentrated equitransferent salt bridge in solvent Z Standard pH PSor pH SSin solvent Z H + sensing el

43、ectrode (hydrogen gas electrode, or glass electrode) (6) E X , E S , etc. are all defined as the difference of the potential of the right-hand (glass electrode) minus the potential of the left-hand electrode (reference electrode). Considering the Nernstian expressions for E Xand E S , the sought pH

44、Xof the sample in question is given by: pH X= pH SS (E X E S )/k + (E JX E JS)/k (7) where k = 2,302 6 RT/F, and E JXand E JSare the liquid junction potentials (see 3.3.2) arising at the junctions between reference electrode and unknown pH Xand between reference electrode and the known standard ph P

45、S , respectively. The concentrated equitransferent salt bridge in solvent Z (see 3.6.5) duly minimizes E JXand E JS,so that their difference (E JX E JS ) (the so-called “residual liquid junction potential”) can be ignored, and the following operational equation is now internationally endorsed for th

46、e determination of pH X : pH X= pH SS (E X E S )/k (8) At extreme acidities or alkalinities, or with high salinities (ionic strengths) of the sample, the residual liquid junction potential may be significant and requires careful consideration for the assessment of the accuracy level of the measured

47、pH X . TR 62434 IEC:2006(E) 7 The cell diagrams (5) and (6), respectively, represent the well known “measure” and “calibration” configurations of the “pH operational cell”. Numerical values for k, the “Nernstian coefficient” or “theoretical slope factor”, at temperatures from (0 to 100) C, are given

48、 in Annex A. Upon aging, the glass electrodes show an irreversible decrease of the slope factor, which thus becomes the “practical slope factor” k k and should consequently be accounted for in the operational equation (8). This is currently accomplished by the “bracketing standards procedure” (or “t

49、wo standards calibration”). This requires use of two standards, one (pH PS1 ) below and one (pH PS2 ) above the expected pH X . The corresponding measurements of E X , E S1 , and E S2 , are then combined to give the following equations: k = (E S2 E S1 )/(pH S2 pH S1 ) (9) pH X= pH S1+ (E X E S1 )(pH S2 pH S1 )/(E S2 E S1 ) (10) 3.3.2 Liquid junction potential Electric potential difference arising across