Insulating liquids - Determination of acidity - Part 3: Test methods for non mineral insulating oils

IEC 62021-3:2014 describes two procedures for the determination of the acidity of unused and used electrical non-mineral insulating oils. Method A is potentiometric titration and Method B is colourimetric titration. The method may be used to indicate relative changes that occur in non-mineral insulating oil during use under oxidizing conditions regardless of the colour or other properties of the resulting non-mineral oil. The acidity can be used in the quality control of unused non-mineral insulating oil. As a variety of oxidation products present in used non-mineral insulating oil contribute to acidity and these products vary widely in their corrosion properties, the test cannot be used to predict corrosiveness of non-mineral insulating oil under service conditions.

Isolierflüssigkeiten - Bestimmung des Säuregehaltes - Teil 3: Prüfverfahren für Isolieröle auf Nichtmineralölbasis

Liquides isolants - Détermination de l'acidité - Partie 3: Méthode d'essai pour les huiles non minérales isolantes

L'IEC 62021-3:2014 décrit deux procédures pour la détermination de l'acidité des huiles non minérales isolantes électriques neuves et usagées. La Méthode A est le titrage potentiométrique et la Méthode B est le titrage colorimétrique. La méthode peut être utilisée pour indiquer des modifications relatives qui se produisent dans une huile non minérale isolante pendant son utilisation par oxydation, indépendamment de la couleur ou d'autres propriétés de l'huile non minérale résultante. L'acidité peut être utilisée dans le contrôle de la qualité de l'huile non minérale isolante neuve. Comme divers produits d'oxydation présents dans l'huile non minérale isolante usagée contribuent à l'acidité et comme ces produits varient largement du point de vue de leurs propriétés de corrosion, l'essai ne peut pas être utilisé pour prévoir la corrosivité d'une huile non minérale isolante dans des conditions de service.

Izolacijske tekočine - Ugotavljanje kislosti - 3. del: Metode za preskušanje nemineralnih (sintetičnih) izolacijskih ol j(IEC 62021-3:2014)

Ta del standarda IEC 62021 opisuje dva postopka za ugotavljanje kislosti neuporabljenih in uporabljenih električnih nemineralnih izolacijskih olj. Metoda A je potenciometrična titracija, metoda B pa kolorimetrična titracija.
OPOMBA 1: Pri neuporabljenih in uporabljenih nemineralnih izolacijskih oljih med sestavine, ki naj bi imele kislinske značilnosti, spadajo organske kisline, fenolne spojine, nekateri produkti oksidacije, smole, organokovinske soli in aditivi.
Metoda se lahko uporablja za označevanje povezanih sprememb nemineralnega izolacijskega olja med uporabo pri oksidativnih pogojih, in sicer ne glede na barvo ali druge lastnosti zadevnega nemineralnega olja.
Kislost se lahko uporabi pri kontroli kakovosti neuporabljenih nemineralnih izolacijskih olj. Ker različni produkti oksidacije v uporabljenih nemineralnih izolacijskih oljih prispevajo h kislosti in imajo različne korozivne lastnosti, se preskus ne more uporabiti za napovedovanje korozivnosti nemineralnega izolacijskega olja pri pogojih obratovanja.
OPOMBA 2: Rezultati kislosti, pridobljeni s potenciometrično preskusno metodo, so lahko enaki rezultatom kolorimetričnih metod ali se razlikujejo, vendar so na splošno enakih razsežnosti.

General Information

Status
Published
Publication Date
13-Nov-2014
Current Stage
6060 - Document made available
Due Date
14-Nov-2014
Completion Date
14-Nov-2014

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SLOVENSKI STANDARD
SIST EN 62021-3:2015
01-maj-2015
,]RODFLMVNHWHNRþLQH8JRWDYOMDQMHNLVORVWLGHO0HWRGH]DSUHVNXãDQMH
QHPLQHUDOQLK VLQWHWLþQLK L]RODFLMVNLKROM ,(&

Insulating liquids - Determination of acidity - Part 3: Test methods for non mineral

insulating oils (IEC 62021-3:2014)

Isolierflüssigkeiten - Bestimmung des Säuregehaltes - Teil 3: Prüfverfahren für Isolieröle

auf Nichtmineralölbasis

Liquides isolants - Détermination de l'acidité - Partie 3: Méthode d'essai pour les huiles

non minérales isolantes
Ta slovenski standard je istoveten z: EN 62021-3:2014
ICS:
29.040.10 Izolacijska olja Insulating oils
SIST EN 62021-3:2015 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN 62021-3:2015
---------------------- Page: 2 ----------------------
SIST EN 62021-3:2015
EUROPEAN STANDARD EN 62021-3
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2014
ICS 29.040.10
English Version
Insulating liquids - Determination of acidity - Part 3: Test
methods for non mineral insulating oils
(IEC 62021-3:2014)

Liquides isolants - Détermination de l'acidité - Partie 3: Isolierflüssigkeiten - Bestimmung des Säuregehaltes - Teil

Méthode d'essai pour les huiles non minérales isolantes 3: Prüfverfahren für Isolieröle auf Nichtmineralölbasis

(CEI 62021-3:2014) (IEC 62021-3:2014)

This European Standard was approved by CENELEC on 2014-04-23. CENELEC members are bound to comply with the CEN/CENELEC

Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC

Management Centre or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the

same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,

Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2014 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN 62021-3:2014 E
---------------------- Page: 3 ----------------------
SIST EN 62021-3:2015
EN 62021-3:2014 - 2 -
Foreword

The text of document 10/936/FDIS, future edition 1 of IEC 62021-3, prepared by IEC TC 10 "Fluids for

electrotechnical applications" was submitted to the IEC-CENELEC parallel vote and approved by

CENELEC as EN 62021-3:2014.
The following dates are fixed:
• latest date by which the document has (dop) 2015-05-14
to be implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2017-04-23
• latest date by which the national
standards conflicting with the
document have to be withdrawn

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent

rights.
Endorsement notice

The text of the International Standard IEC 62021-3:2014 was approved by CENELEC as a European

Standard without any modification.
---------------------- Page: 4 ----------------------
SIST EN 62021-3:2015
- 3 - EN 62021-3:2014
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod), the relevant EN/HD

applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:

www.cenelec.eu
Publication Year Title EN/HD Year
IEC 60475 - Method of sampling insulating liquids EN 60475 -
ISO 5725 series Accuracy (trueness and precision) of - series
measurement methods and results
ISO 6619 - Petroleum products and lubricants; - -
neutralization number; potentiometric
titration method
---------------------- Page: 5 ----------------------
SIST EN 62021-3:2015
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SIST EN 62021-3:2015
IEC 62021-3
Edition 1.0 2014-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Insulating liquids – Determination of acidity –
Part 3: Test methods for non-mineral insulating oils
Liquides isolants – Détermination de l’acidité –
Partie 3: Méthodes d’essai pour les huiles non minérales isolantes
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX T
ICS 29.040.10 ISBN 978-2-8322-1404-6

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 7 ----------------------
SIST EN 62021-3:2015
– 2 – IEC 62021-3:2014 © IEC 2014
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 Method A: Automatic potentiometric titration .................................................................... 8

4.1 Principle ............................................................................................................ 8

4.2 Reagents and auxiliary products ........................................................................ 8

4.2.1 Reagents .......................................................................................... 8

4.2.2 Titration reagent ............................................................................... 8

4.2.3 Titration solvent ................................................................................ 8

4.2.4 Potassium hydrogen phthalate, primary standard .............................. 9

4.2.5 Reference electrode electrolyte ........................................................ 9

4.2.6 Aqueous buffer solutions .................................................................. 9

4.2.7 Glass electrode cleaning solution ..................................................... 9

4.3 Apparatus .......................................................................................................... 9

4.3.1 Potentiometric titration apparatus ..................................................... 9

4.3.2 Glass indicator electrode .................................................................. 9

4.3.3 Reference electrode ....................................................................... 10

4.3.4 Stirrer ............................................................................................. 10

4.3.5 Titration vessel ............................................................................... 10

4.3.6 Titration stand ................................................................................ 10

4.4 Sampling.......................................................................................................... 10

4.5 Preparation and maintenance of electrode system ........................................... 10

4.5.1 Preparation ..................................................................................... 10

4.5.2 Maintenance ................................................................................... 10

4.6 Calibration ....................................................................................................... 11

4.6.1 Calibration of pH titrimeter .............................................................. 11

4.6.2 Settings for the potentiometric instrument ....................................... 11

4.7 Procedure ........................................................................................................ 12

4.7.1 General .......................................................................................... 12

4.7.2 Standardization of alcoholic potassium hydroxide solution .............. 12

4.7.3 Blank titration ................................................................................. 13

4.7.4 Sample titration .............................................................................. 13

4.8 Calculation of result ......................................................................................... 14

4.9 Precision .......................................................................................................... 14

4.9.1 Repeatability .................................................................................. 14

4.9.2 Reproducibility ................................................................................ 14

4.10 Report.............................................................................................................. 15

5 Method B: Colourimetric titration.................................................................................... 15

5.1 Principle .......................................................................................................... 15

5.2 Reagents ......................................................................................................... 15

5.2.1 General .......................................................................................... 15

5.2.2 Titration reagent ............................................................................. 15

5.2.3 Titration solvent .............................................................................. 16

5.2.4 Potassium hydrogen phthalate, primary standard ............................ 16

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SIST EN 62021-3:2015
IEC 62021-3:2014 © IEC 2014 – 3 –

5.2.5 Standard hydrochloric acid solution ................................................ 16

5.2.6 Alkali blue 6B indicator solution ...................................................... 16

5.2.7 Cobalt nitrate solution ..................................................................... 16

5.3 Apparatus ........................................................................................................ 16

5.3.1 Titration vessel ............................................................................... 16

5.3.2 Stirrer ............................................................................................. 16

5.3.3 Burette ........................................................................................... 16

5.4 Sampling.......................................................................................................... 16

5.5 Procedure ........................................................................................................ 17

5.5.1 General .......................................................................................... 17

5.5.2 Standardization of alcoholic potassium hydroxide solution .............. 17

5.5.3 Blank titration ................................................................................. 17

5.5.4 Sample titration .............................................................................. 18

5.6 Calculation of result ......................................................................................... 18

5.7 Precision .......................................................................................................... 18

5.7.1 Repeatability .................................................................................. 18

5.7.2 Reproducibility ................................................................................ 19

5.8 Report.............................................................................................................. 19

Annex A (informative) Determination of acidity in non-mineral electrical insulating oils

by photometric titration ......................................................................................................... 20

A.1 Principle .......................................................................................................... 20

A.2 Reagents and solvents ..................................................................................... 20

A.3 Preparation of titration solutions and solvents .................................................. 20

A.3.1 Potassium hydroxide alcoholic solution (0,01 mol/l) ........................ 20

A.3.2 Potassium hydrogen phthalate solution (0,01 mol/l) ........................ 20

A.3.3 Titration solvent .............................................................................. 21

A.4 Apparatus ........................................................................................................ 21

A.4.1 Volumetric titrator ........................................................................... 21

A.4.2 Titration vessel ............................................................................... 21

A.4.3 Titration stand ................................................................................ 21

A.4.4 Stirrer ............................................................................................. 21

A.4.5 Recorder/printer ............................................................................. 21

A.4.6 Photometric sensor ......................................................................... 21

A.5 Sampling.......................................................................................................... 22

A.6 Procedure ........................................................................................................ 22

A.6.1 Preparation and maintenance of the titration system ....................... 22

A.6.2 Determination of acidity of the titration solvent (blank titration) ....... 22

A.6.3 Determination of molarity of the potassium hydroxide alcoholic

solution (0,01 mol/l) ........................................................................ 22

A.6.4 Titration of soluble acidity in the oil sample..................................... 23

A.7 Calculation of result ......................................................................................... 23

A.8 Report.............................................................................................................. 23

Figure 1 – Potentiometric titration curve ................................................................................ 12

Figure A.1 – Molecular structure of para-naphtholbenzein indicator in a) acidic media

and b) basic media ............................................................................................................... 24

Figure A.2 – UV spectra of para-naphtholbenzein indicator in toluene/2-propanol/water

solution in acidic media (curve a) and basic media (curve b) ................................................. 24

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SIST EN 62021-3:2015
– 4 – IEC 62021-3:2014 © IEC 2014
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATING LIQUIDS – DETERMINATION OF ACIDITY –
Part 3: Test methods for non-mineral insulating oils
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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

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.

International Standard IEC 62021-3 has been prepared by IEC technical committee 10: Fluids

for electrotechnical applications.
The text of this standard is based on the following documents:
FDIS Report on voting
10/936/FDIS 10/942/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.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the IEC 62021 series, published under the general title Insulating liquids –

Determination of acidity, can be found on the IEC website.
---------------------- Page: 10 ----------------------
SIST EN 62021-3:2015
IEC 62021-3:2014 © IEC 2014 – 5 –

The committee has decided that the contents of this publication will remain unchanged until

the stability 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.

IMPORTANT – The “colour inside” logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct understanding

of its contents. Users should therefore print this publication using a colour printer.

---------------------- Page: 11 ----------------------
SIST EN 62021-3:2015
– 6 – IEC 62021-3:2014 © IEC 2014
INTRODUCTION
Health and safety

This International Standard does not purport to address all the safety problems associated

with its use. It is the responsibility of the user of the standard to establish appropriate health

and safety practices and determine the applicability of regulatory limitations prior to use.

The insulating liquids which are the subject of this standard should be handled with due

regard to personal hygiene. Direct contact with the eyes may cause slight irritation. In the

case of eye contact, irrigation with copious quantities of clean running water should be carried

out and medical advice sought.

Some of the procedures referenced in this standard involve the use of processes that could

lead to a hazardous situation. Attention is drawn to the relevant standard for guidance.

Environment

This standard involves non-mineral insulating oils, chemicals, used sample containers and

fluid-contaminated solids. The disposal of these items should be carried out according to local

regulations with regard to their impact on the environment. Every precaution should be taken

to prevent the release into the environment of these oils.
---------------------- Page: 12 ----------------------
SIST EN 62021-3:2015
IEC 62021-3:2014 © IEC 2014 – 7 –
INSULATING LIQUIDS – DETERMINATION OF ACIDITY –
Part 3: Test methods for non-mineral insulating oils
1 Scope

This part of IEC 62021 describes two procedures for the determination of the acidity of

unused and used electrical non-mineral insulating oils. Method A is potentiometric titration

and Method B is colourimetric titration.

NOTE 1 In unused and used non-mineral insulating oils, the constituents that may be considered to have acidic

characteristics include organic acids, phenolic compounds, some oxidation products, resins, organometallic salts

and additives.

The method may be used to indicate relative changes that occur in non-mineral insulating oil

during use under oxidizing conditions regardless of the colour or other properties of the

resulting non-mineral oil.

The acidity can be used in the quality control of unused non-mineral insulating oil.

As a variety of oxidation products present in used non-mineral insulating oil contribute to

acidity and these products vary widely in their corrosion properties, the test cannot be used to

predict corrosiveness of non-mineral insulating oil under service conditions.

NOTE 2 The acidity results obtained by potentiometric test method may or may not be numerically the same as

those obtained by colourimetric methods, but they are generally of the same magnitude.

2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60475, Method of sampling insulating liquids

ISO 5725 (all parts), Accuracy (trueness and precision) of measurement methods and results

ISO 6619, Petroleum products and lubricants – Neutralization number – Potentiometric

titration method
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
acidity

quantity of base, expressed in milligrams of potassium hydroxide per gram of sample,

required to titrate potentiometrically or colourimetrically a test portion in a specified solvent to

the end point
3.2
non-mineral insulating oil
insulating liquid, not derived from petroleum crudes
---------------------- Page: 13 ----------------------
SIST EN 62021-3:2015
– 8 – IEC 62021-3:2014 © IEC 2014
3.3
unused oil

non-mineral insulating oil that has not been used in, or been in contact with, electrical

equipment
4 Method A: Automatic potentiometric titration
4.1 Principle

Any acid-base titration may be conducted potentiometrically. The test portion of the insulating

fluid is dissolved in solvent and titrated potentiometrically with alcoholic potassium hydroxide

using a glass-indicating electrode and a reference electrode. The potential difference (which

can be expressed as pH after calibration) is measured after the successive addition of known

increments of alcoholic potassium hydroxide.

Where a strong point of inflection is detected from the first derivative of the titration curve, this

should be used as the end point. If only a weak inflection point is present, the potential

difference corresponding to pH of 11,5 has been found more reproducible and less
instrument-dependent.
4.2 Reagents and auxiliary products
4.2.1 Reagents

Only reagents of recognized analytical grade and de-ionized water or water of equivalent

purity shall be used.
4.2.2 Titration reagent

Standard alcoholic solution between 0,01 mol/l and 0,05 mol/l potassium hydroxide (KOH).

EXAMPLE Preparation of 0,01 mol/l potassium hydroxide in 2-propanol.

Add 0,6 g of potassium hydroxide to 1 000 ml ± 10 ml of 2-propanol. Boil gently for 10 min to

effect solution. Cool and stopper the flask.

Allow the solution to stand in the dark for 2 days and then filter the supernatant liquid through

a 5 µm membrane filter. Store in a suitable amber glass bottle.

The concentration of this solution is approximately 0,01 mol/l and shall be standardized as

described in 4.7.2.

Store in such a manner that the solution is protected from atmospheric carbon dioxide by

means of a guard tube containing soda-lime absorbent and in such a way that it does not

come into contact with cork, rubber or saponifiable stopcock grease.

Commercial alcoholic potassium hydroxide solution may be used, if necessary diluting to

0,01 mol/l with 2-propanol. This shall be standardized as described in 4.7.2.

NOTE 1 For oils with high acidity, which may give an extended titration time, it may be helpful to carry out a pre-

test using 0,1 mol/l potassium hydroxide titrant to determine a suitable titrant concentration.

NOTE 2 For periodic tests on equipment in service, faster titration may be achieved by the use of 0,05 or

0,1 mol/l potassium hydroxide by agreement between the laboratory and the equipment owner, although this may

result in poorer precision and detection limit.
4.2.3 Titration solvent
The titration solvent is as follows:
---------------------- Page: 14 ----------------------
SIST EN 62021-3:2015
IEC 62021-3:2014 © IEC 2014 – 9 –
– 2-propanol (isopropanol, IPA), pure.

2-propanol is the preferred solvent. It should be noted that the use of other solvents might

change the dissociation potential and thus the neutralisation point.
4.2.4 Potassium hydrogen phthalate, primary standard
This should be dried before use for 2 h at 105 °C.

A 0,1 mol/l solution of hydrochloric acid in de-ionized water, prepared as in ISO 6619, may be

used. Other acids may be used, e.g. benzoic acid, provided they are certified against a

primary standard.
4.2.5 Reference electrode electrolyte

Prepare a solution of potassium chloride in de-ionized water, or lithium chloride in ethanol, at

the concentration recommended by the electrode manufacturer. Commercially available

solutions may be used where available.
4.2.6 Aqueous buffer solutions

Buffer solutions of suitable pH for calibration of electrodes, for example, pH 4, pH 7 and

pH 11 or close to pH 12.
4.2.7 Glass electrode cleaning solution

Weigh 8 g of ammonium peroxydisulfate into a glass beaker. Carefully add 100 ml of 98 %

sulphuric acid and gently stir. Before use, the solution should be left overnight for the solid to

dissolve completely.

WARNING Ammonium peroxydisulfate is a strong oxidizing agent. Sulphuric acid is a strong

corrosive agent. Handle carefully.

Commercially available cleaning solutions as recommended by the electrode manufacturer

may be used.
4.3 Apparatus
4.3.1 Potentiometric titration apparatus

An automatic pH titrimeter or an instrument for a potentiometric titration capable of titrating to

a fixed end-point using either variable or fixed titrant increments.

The instrument shall be protected from stray electrical fields so that no change of the reading

is produced by touching any part of the system with a grounded lead.
An automatic burette with a dis
...

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