Animal and vegetable fats and oils - Determination of acid value and acidity (ISO 660:2020)

This document specifies three methods (two titrimetric and one potentiometric) for the determination
of acidity in animal and vegetable fats and oils, hereinafter referred to as “fats”. The acidity is expressed
preferably as acid value or, alternatively, as acidity calculated conventionally.
This document is applicable to refined and crude vegetable or animal fats and oils, soap stock fatty
acids or technical fatty acids. It does not apply to waxes.
Since the methods are completely non-specific, they do not apply to differentiating between mineral
acids, free fatty acids and other organic acids. The acid value, therefore, includes any mineral acids that
are present.
Milk and milk products (or fat coming from milk and milk products) are excluded from the Scope of this
document.

Tierische und pflanzliche Fette und Öle - Bestimmung der Säurezahl und der Azidität (ISO 660:2020)

Dieses Dokument legt drei Verfahren (zwei titrimetrische und ein potentiometrisches) zur Bestimmung der Azidität in tierischen und pflanzlichen Fetten und Ölen, die im Folgenden als „Fette“ bezeichnet werden, fest. Die Azidität wird vorzugsweise als Säurezahl ausgedrückt oder alternativ als konventionell berechnete Azidität.
Dieses Dokument gilt für raffinierte und rohe pflanzliche oder tierische Fette und Öle, Soapstock-Fettsäuren oder technische Fettsäuren. Es gilt nicht für Wachse.
Da die Verfahren vollkommen unspezifisch sind, gelten sie nicht zur Unterscheidung zwischen Mineralsäuren, freien Fettsäuren und sonstigen organischen Säuren. Die Säurezahl schließt daher alle vorhandenen Mineralsäuren ein.
Milch und Milcherzeugnisse (oder Fett aus Milch und Milcherzeugnissen) sind vom Anwendungsbereich dieses Dokumentes ausgenommen.

Corps gras d'origines animale et végétale - Détermination de l'indice d'acide et de l'acidité (ISO 660:2020)

Le présent document spécifie trois méthodes (deux titrimétriques et une potentiométrique) pour la détermination de l'acidité dans les corps gras d'origines animale et végétale dits «corps gras». L'acidité est exprimée, de préférence, en indice d'acide ou bien en acidité calculée conventionnellement.
Le présent document est applicable aux corps gras d'origines végétale ou animale à l'état brut ou raffinés, aux acides gras des pâtes de neutralisation ou aux acides gras de qualité technique. Il ne s'applique pas aux cires.
Ces méthodes ne sont en aucun cas spécifiques, elles ne s'appliquent donc pas à la différenciation des acides minéraux, acides gras libres et autres acides organiques. De ce fait, l'indice d'acide inclut tout acide minéral présent.
Le lait et les produits laitiers (ou la matière grasse issue du lait et des produits laitiers) sont exclus du domaine d'application du présent document.

Rastlinske in živalske maščobe in olja - Določevanje kislinskega števila in kislosti (ISO 660:2020)

General Information

Status
Published
Public Enquiry End Date
04-Sep-2019
Publication Date
12-Oct-2020
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
08-Oct-2020
Due Date
13-Dec-2020
Completion Date
13-Oct-2020

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SLOVENSKI STANDARD
SIST EN ISO 660:2020
01-november-2020
Nadomešča:
SIST EN ISO 660:2009
Rastlinske in živalske maščobe in olja - Določevanje kislinskega števila in kislosti
(ISO 660:2020)
Animal and vegetable fats and oils - Determination of acid value and acidity (ISO
660:2020)
Tierische und pflanzliche Fette und Öle - Bestimmung der Säurezahl und der Azidität
(ISO 660:2020)
Corps gras d'origines animale et végétale - Détermination de l'indice d'acide et de
l'acidité (ISO 660:2020)
Ta slovenski standard je istoveten z: EN ISO 660:2020
ICS:
67.200.10 Rastlinske in živalske Animal and vegetable fats
maščobe in olja and oils
SIST EN ISO 660:2020 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 660:2020

---------------------- Page: 2 ----------------------
SIST EN ISO 660:2020


EN ISO 660
EUROPEAN STANDARD

NORME EUROPÉENNE

September 2020
EUROPÄISCHE NORM
ICS 67.200.10 Supersedes EN ISO 660:2009
English Version

Animal and vegetable fats and oils - Determination of acid
value and acidity (ISO 660:2020)
Corps gras d'origines animale et végétale - Tierische und pflanzliche Fette und Öle - Bestimmung
Détermination de l'indice d'acide et de l'acidité (ISO der Säurezahl und der Azidität (ISO 660:2020)
660:2020)
This European Standard was approved by CEN on 28 August 2020.

CEN 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 CEN
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 CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 660:2020 E
worldwide for CEN national Members.

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SIST EN ISO 660:2020
EN ISO 660:2020 (E)
Contents Page
European foreword . 3

2

---------------------- Page: 4 ----------------------
SIST EN ISO 660:2020
EN ISO 660:2020 (E)
European foreword
This document (EN ISO 660:2020) has been prepared by Technical Committee ISO/TC 34 "Food
products" in collaboration with Technical Committee CEN/TC 307 “Oilseeds, vegetable and animal fats
and oils and their by-products - Methods of sampling and analysis” the secretariat of which is held by
AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2021, and conflicting national standards shall
be withdrawn at the latest by March 2021.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 660:2009.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 660:2020 has been approved by CEN as EN ISO 660:2020 without any modification.

3

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SIST EN ISO 660:2020

---------------------- Page: 6 ----------------------
SIST EN ISO 660:2020
INTERNATIONAL ISO
STANDARD 660
Fourth edition
2020-03
Animal and vegetable fats and oils —
Determination of acid value and acidity
Corps gras d'origines animale et végétale — Détermination de l'indice
d'acide et de l'acidité
Reference number
ISO 660:2020(E)
©
ISO 2020

---------------------- Page: 7 ----------------------
SIST EN ISO 660:2020
ISO 660:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

---------------------- Page: 8 ----------------------
SIST EN ISO 660:2020
ISO 660:2020(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus . 3
7 Sampling . 3
8 Preparation of test sample . 3
9 Procedure. 3
9.1 Cold solvent method using indicator (reference method) . 3
9.2 Cold solvent method using potentiometric titration (reference method) . 4
9.3 Hot ethanol method using indicator . 4
10 Calculation . 5
10.1 General . 5
10.2 Acid value. 5
10.3 Acidity or free fatty acid content . 5
11 Precision . 6
11.1 Repeatability . 6
11.2 Reproducibility . 6
12 Test report . 6
Annex A (informative) Results of interlaboratory tests. 7
Annex B (informative) Comparison of three coloured indicators .10
Bibliography .12
© ISO 2020 – All rights reserved iii

---------------------- Page: 9 ----------------------
SIST EN ISO 660:2020
ISO 660:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 11,
Animal and vegetable fats and oils, , in collaboration with the European Committee for Standardization
(CEN) Technical Committee CEN/TC 307, Oilseeds, vegetable and animal fats and oils and their by-
products — Methods of sampling and analysis, in accordance with the Agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 660:2009), which has been technically
revised. The main changes compared with the previous edition are as follows:
— a non-applicability statement for milk and milk products has been added to the Scope because
ISO 1740 applies in these cases;
— details of a CMR classification on coloured indicators have been added;
— data from the collaborative trial carried out to support this modification have been added in
Annex B.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

---------------------- Page: 10 ----------------------
SIST EN ISO 660:2020
INTERNATIONAL STANDARD ISO 660:2020(E)
Animal and vegetable fats and oils — Determination of acid
value and acidity
1 Scope
This document specifies three methods (two titrimetric and one potentiometric) for the determination
of acidity in animal and vegetable fats and oils, hereinafter referred to as “fats”. The acidity is expressed
preferably as acid value or, alternatively, as acidity calculated conventionally.
This document is applicable to refined and crude vegetable or animal fats and oils, soap stock fatty
acids or technical fatty acids. It does not apply to waxes.
Since the methods are completely non-specific, they do not apply to differentiating between mineral
acids, free fatty acids and other organic acids. The acid value, therefore, includes any mineral acids that
are present.
Milk and milk products (or fat coming from milk and milk products) are excluded from the Scope of this
document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
ISO 385, Laboratory glassware — Burettes
ISO 661, Animal and vegetable fats and oils — Preparation of test sample
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 3696, Water for analytical laboratory use — Specification and test methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
acid value
number of milligrams of potassium hydroxide required to neutralize the free fatty acids present in 1 g
of fat, when determined in accordance with the procedure specified in this document
Note 1 to entry: The acid value is expressed in milligrams per gram.
3.2
acidity
content of free fatty acids determined according to the procedure specified in this document
Note 1 to entry: The acidity is expressed as a percentage by mass. If the result of the determination is reported as
acidity without further explanation, this is, by convention, the acidity based on the oleic acid content.
© ISO 2020 – All rights reserved 1

---------------------- Page: 11 ----------------------
SIST EN ISO 660:2020
ISO 660:2020(E)

4 Principle
The sample is dissolved in a suitable solvent mixture, and the acids present are titrated with an
ethanolic or methanolic solution of sodium or potassium hydroxide.
The methods specified in 9.1 and 9.2 are reference methods.
5 Reagents
WARNING — Attention is drawn to regulations that specify the handling of hazardous substances.
Technical, organizational and personal safety measures shall be followed.
Use only reagents of recognized analytical grade, unless otherwise specified.
5.1 Solvent A for the solvent mixture (5.3), ethanol, volume fraction, φ ≈ 96 %.
As a replacement, propan-2-ol, volume fraction, φ ≈ 99 %, may be used.
5.2 Solvent
...

SLOVENSKI STANDARD
oSIST prEN ISO 660:2019
01-september-2019
Rastlinske in živalske maščobe in olja - Določevanje kislinskega števila in kislosti
(ISO/DIS 660:2019)
Animal and vegetable fats and oils - Determination of acid value and acidity (ISO/DIS
660:2019)
Tierische und pflanzliche Fette und Öle - Bestimmung der Säurezahl und der Azidität
(ISO/DIS 660:2019)
Corps gras d'origines animale et végétale - Détermination de l'indice d'acide et de
l'acidité (ISO/DIS 660:2019)
Ta slovenski standard je istoveten z: prEN ISO 660
ICS:
67.200.10 Rastlinske in živalske Animal and vegetable fats
maščobe in olja and oils
oSIST prEN ISO 660:2019 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
oSIST prEN ISO 660:2019

---------------------- Page: 2 ----------------------
oSIST prEN ISO 660:2019
DRAFT INTERNATIONAL STANDARD
ISO/DIS 660
ISO/TC 34/SC 11 Secretariat: BSI
Voting begins on: Voting terminates on:
2019-05-29 2019-08-21
Animal and vegetable fats and oils — Determination of acid
value and acidity
Corps gras d'origines animale et végétale — Détermination de l'indice d'acide et de l'acidité
ICS: 67.200.10
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 660:2019(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2019

---------------------- Page: 3 ----------------------
oSIST prEN ISO 660:2019
ISO/DIS 660:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

---------------------- Page: 4 ----------------------
oSIST prEN ISO 660:2019
ISO/DIS 660:2019(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus . 3
7 Sampling . 3
8 Preparation of test sample . 3
9 Procedure. 3
9.1 Cold solvent method using indicator (Reference method) . 3
9.2 Cold solvent method using potentiometric titration (Reference method). 4
9.3 Hot ethanol method using indicator . 4
10 Calculation . 5
10.1 Acid value. 5
10.2 Acidity or free fatty acid content . 5
11 Precision . 6
11.1 Repeatability . 6
11.2 Reproducibility . 6
12 Test report . 6
Annex A (informative) Results of interlaboratory tests. 7
Annex B (informative) Comparison of three coloured indicators . 9
Bibliography .11
© ISO 2019 – All rights reserved iii

---------------------- Page: 5 ----------------------
oSIST prEN ISO 660:2019
ISO/DIS 660:2019(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 34, Food Products, Subcommittee SC 11,
Animal and vegetable fats and oils.
This fourth edition cancels and replaces the third edition (ISO 660:2009), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— Addition of a non‐applicability statement for milk and milk products to the scope as ISO 1740
"Milkfat products and butter – Determination of fat acidity (Reference method)" applies,
— Additions of details on CMR classification on coloured indicators,
— Additions in Annex of data from the collaborative trial carried out to support this modification.
iv © ISO 2019 – All rights reserved

---------------------- Page: 6 ----------------------
oSIST prEN ISO 660:2019
DRAFT INTERNATIONAL STANDARD ISO/DIS 660:2019(E)
Animal and vegetable fats and oils — Determination of acid
value and acidity
1 Scope
This International Standard specifies three methods (two titrimetric and one potentiometric) for the
determination of the acidity in animal and vegetable fats and oils, hereinafter referred to as fats. The
acidity is expressed preferably as acid value, or alternatively as acidity calculated conventionally.
This International Standard is applicable to refined and crude vegetable or animal fats and oils, soap
stock fatty acids or technical fatty acids. The methods are not applicable to waxes.
Since the methods are completely non‐specific, they cannot be used to differentiate between mineral
acids, free fatty acids, and other organic acids. The acid value, therefore, also includes any mineral acids
that may be present.
Milk and milk products (or fat coming from milk and milk products) are excluded from the scope of
ISO 660.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
ISO 661, Animal and vegetable fats and oils — Preparation of test sample
ISO 3696, Water for analytical laboratory use — Specification and test methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain
terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
acid value
number of milligrams of potassium hydroxide required to neutralize the free fatty acids present in 1 g
of fat, when determined in accordance with the procedure specified in this International Standard
Note 1 to entry: The acid value is expressed in milligrams per gram.
3.2
acidity
content of free fatty acids determined according to the procedure specified in this International
Standard
Note 1 to entry: The acidity is expressed as a percentage by mass. If the result of the determination is reported as
acidity without further explanation, this is, by convention, the acidity based on the oleic acid content.
© ISO 2019 – All rights reserved 1

---------------------- Page: 7 ----------------------
oSIST prEN ISO 660:2019
ISO/DIS 660:2019(E)

4 Principle
The sample is dissolved in a suitable solvent mixture, and the acids present are titrated with an
ethanolic or methanolic solution of potassium or sodium hydroxide.
The methods specified in 9.1 and 9.2 are reference methods.
5 Reagents
WARNING — Attention is drawn to the regulations which specify the handling of hazardous
substances. Technical, organizational and personal safety measures shall be followed.
Use only reagents of recognized analytical grade, unless otherwise specified.
5.1 Solvent A for solvent mixture (5.3): ethanol, volume fraction, φ ≈ 96 %.
As a replacement, propan-2-ol, volume fraction, φ ≈ 99 %, can be used.
5.2 Solvent B for solvent mixture (5.3): diethyl ether, peroxide‐free.
As a replacement, tert‐butyl methyl ether, light petroleum (boiling range 40 °C to 60 °C) or toluene can
be used.
WARNING — Diethyl ether is very flammable and may form explosive peroxides. Use with great
caution.
5.3 Solvent mixture, mix equal volumes of solvent A and B, (e.g. φ = 50 ml/100 ml and
A
φ = 50 ml/100 ml).
B
For hard or animal fats, a solvent mixture of one volume of solvent A (e.g. 25 ml) and three volumes of
tert‐butyl methyl ether or toluene (e.g. 75 ml) is recommended.
Neutralize, just before use, by adding potassium hydroxide solution in the presence of 0,3 ml of the
coloured indicator solution per 100 ml of solvent mixture.
For the titration with aqueous KOH, the solvent propan‐2‐ol can be used.
5.4 Ethanol or methanol, of minimum volume fraction, φ = 95 %.
5.5 Sodium hydroxide or potassium hydroxide, ethanolic or methanolic standard volumetric
solutions, amount of substance concentration c(NaOH) or c(KOH) = 0,1 mol/l and 0,5 mol/l. The
concentration shall be checked with a standard volumetric HCl solution.
NOTE The ethanolic/methanolic sodium/potassium hydroxide solution can be replaced by an aqueous
sodium/potassium hydroxide solution, but only if the volume of water introduced does not lead to phase
separation.
5.6 Thymolphthalein or Alkali blue 6B, solution in ethanol, mass concentration, ρ = 2 g/100 ml or,
failing that, Phenolphthalein solution in ethanol, mass concentration, ρ = 1 g/100 ml (CAS number:
1324-80-7).
NOTE 1 Ph
...

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