SIST ISO 6488:2021

INTERNATIONAL ISO
STANDARD 6488
Third edition
2021-06
Tobacco and tobacco products —
Determination of water content —
Karl Fischer method
Tabac et produits du tabac — Détermination de la teneur en eau —
Méthode de Karl Fischer
Reference number
©
ISO 2021
© ISO 2021
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus . 2
7 Standardization of the Karl Fischer reagent . 2
8 Sampling . 3
9 Procedure. 3
9.1 Sample handling . 3
9.2 Test portion . 3
9.3 Preparation of titration apparatus . 4
9.4 Blank test . 4
9.5 Determination . 4
10 Expression of results . 5
11 Repeatability and reproducibility . 5
12 Test report . 6
Bibliography . 8
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 126, Tobacco and tobacco products.
This third edition cancels and replaces the second edition (ISO 6488:2004), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 6488:2004/Cor 1:2008.
The main changes compared to the previous edition are as follows:
— the term high-moisture tobacco has been deleted;
— further information on interlaboratory testing including additional sample types and corresponding
statistical data have been added.
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 2021 – All rights reserved

Introduction
This document specifies a Karl Fischer method for the determination of the water content of tobacco
and tobacco products. Independent collaborative studies were conducted in 2002, 2009, and 2018. This
method is applicable to ground tobacco, a range of smokeless tobacco products, cigarette filler and
ground cigars.
INTERNATIONAL STANDARD ISO 6488:2021(E)
Tobacco and tobacco products — Determination of water
content — Karl Fischer method
1 Scope
This document specifies a method for the determination of water content by the Karl Fischer method. It
is applicable to raw tobacco as well as tobacco taken from finished products. The method is suitable for
water contents ranging from a mass fraction of at least 2 % to 55 %.
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 648, Laboratory glassware — Single-volume pipettes
ISO 3696, Water for analytical laboratory use — Specification and test methods
3 Terms and definitions
No terms and definitions are listed in this document.
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 https:// www .electropedia .org/
4 Principle
The water content of a sample of tobacco or a tobacco product is determined, using the volumetric
procedure, by extraction of water by shaking the sample with dry methanol, followed by injection of an
aliquot portion into the titration vessel, titration with pyridine-free Karl Fischer reagent and calculation
of the water content. The results are reported as mass percent (%).
If a size reduction (grinding or cutting) is applied, it can create a decrease in the original water content.
Cryogenic techniques may be used to prevent such moisture losses.
5 Reagents
Use only reagents of recognized analytical grade.
5.1 Karl Fischer reagent, free from pyridine, having a water equivalent per millilitre of reagent of
approximately 2 mg to 5 mg.
5.2 Methanol, with a water content of less than 0,05 g per 100 g.
Methanol is hygroscopic so it is recommended to cap the bottle with an automatic delivery pipette
equipped with drying tube.
5.3 Desiccant, silica gel, freshly activated.
5.4 Water, in accordance with grade 2 of ISO 3696, or better.
6 Apparatus
Usual laboratory apparatus and, in particular, the following items.
All glassware used in the preparation and in the water determination shall be heated at (105 ± 5) °C
for at least 1 h after visible water has evaporated. The glassware shall then be cooled and stored in a
desiccator over desiccant (5.3) until used.
6.1 Karl Fischer apparatus for automatic titration, consisting of items 6.1.1 to 6.1.5.
6.1.1 Apparatus for the detection of the titration end point, according to the biamperiometrical
method.
6.1.2 Double electrode, made of platinum.
6.1.3 Magnetic stirrer.
6.1.4 Titration vessel.
6.1.5 Automatic burettes, for methanol and Karl Fischer reagent.
6.2 Mechanical shaker, rotary platform, adjustable to a shaking frequency suitable for vigorous
mixing.
6.3 Microsyringe, for the determination of the water equivalent, of capacity 50 µl.
6.4 Glass volumetric pipettes, class A, of capacities 10 ml and 20 ml, in accordance with ISO 648.
6.5 Conical flasks, of capacities 250 ml and 500 ml, with a conical ground glass joint.
6.6 Hot-air oven, capable of maintaining a temperature of (105 ± 5) °C.
7 Standardization of the Karl Fischer reagent
Add sufficient methanol (5.2) to the titration vessel (6.1.4) to immerse the tips of the electrodes. Titrate
any residual solution (see NOTE) in the titration vessel to its end point by addition of Karl Fischer
reagent (5.1).
Add 50 µl of water to the titration vessel using the microsyringe (6.3). To ensure that the syringe does
not contain air bubbles, fill it to above the 50 µl mark, invert it and tap the air bubbles to the top. Then
depress the plunger to the 50 µl mark and remove excess water quickly from the needle tip with a
tissue. As an alternative, fill the syringe with 50 µl of water and weigh the syringe. After dosage, weigh
the syringe again and note the exact mass of water.
Transfer the 50 µl of water to the titration vessel, taking care to inject the water directly into the
solution, not allowing any to fall onto the neck or walls of the vessel. Where the vessel can be fitted with
a rubber membrane cap, this shall be used and the needle inserted through the cap. If a water droplet
remains on the needle tip, remove it by touching the surface of the solution in the vessel.
Titrate with Karl Fischer reagent (5.1) and record the titration value. Repeat the process. If the
difference between the values of two determinations is not greater than 0,05 ml, take the mean of two
determinations. Otherwise, repeat the whole determination.
2 © ISO 2021 – All rights reserved

Standardize the Karl Fischer reagent every working day.
For best results with the Karl Fischer technique, it is important to ensure that all stages of the analysis
are carried out in a uniform manner, extract to extract, sample to sample, day to day.
NOTE It is common practice with the direct titration technique to carry out a titration “on top” of residual
solution in the titration vessel, i.e. without removing the residual solution. When the volume in the vessel
reaches a certain level, the liquid is run to waste, retaining just enough for the electrode tips to be immersed.
In time, however, the methanol concentration in the vessel falls to a level such that the reaction cannot proceed
satisfactorily. A precipitate can form and false titration values can be obtained. Only experience will tell when
titration “on top of” residual solution has reached this point, and then the titration vessel has to be completely
emptied to waste, rinsed, and recharged with methanol.
Calculate the water equivalent of the Karl Fischer reagent according to Formula (1):
m
w
E = (1)
V
w
where
E is the water equivalent, in milligrams of water per millilitre of reagent;
m is the mass, in milligrams, of the water used for the standardization of
...

INTERNATIONAL ISO
STANDARD 6488
Third edition
2021-06
Corrected version
2021-10
Tobacco and tobacco products —
Determination of water content —
Karl Fischer method
Tabac et produits du tabac — Détermination de la teneur en eau —
Méthode de Karl Fischer
Reference number
© ISO 2021
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus . 2
7 Standardization of the Karl Fischer reagent . 2
8 Sampling . 3
9 Procedure .3
9.1 Sample handling . 3
9.2 Test portion . 4
9.3 Preparation of titration apparatus . 4
9.4 Blank test . 4
9.5 Determination . 4
10 Expression of results . 5
11 Repeatability and reproducibility .5
12 Test report . 6
Bibliography . 8
iii
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 126, Tobacco and tobacco products.
This third edition cancels and replaces the second edition (ISO 6488:2004), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 6488:2004/Cor 1:2008.
The main changes compared to the previous edition are as follows:
— the term high-moisture tobacco has been deleted;
— further information on interlaboratory testing including additional sample types and corresponding
statistical data have been added.
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.
This corrected version of ISO 6488:2021 incorporates the following correction:
— a warning for the safe handling of methanol has been added in 5.2.
iv
Introduction
This document specifies a Karl Fischer method for the determination of the water content of tobacco
and tobacco products. Independent collaborative studies were conducted in 2002, 2009, and 2018. This
method is applicable to ground tobacco, a range of smokeless tobacco products, cigarette filler and
ground cigars.
v
INTERNATIONAL STANDARD ISO 6488:2021(E)
Tobacco and tobacco products — Determination of water
content — Karl Fischer method
1 Scope
This document specifies a method for the determination of water content by the Karl Fischer method. It
is applicable to raw tobacco as well as tobacco taken from finished products. The method is suitable for
water contents ranging from a mass fraction of at least 2 % to 55 %.
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 648, Laboratory glassware — Single-volume pipettes
ISO 3696, Water for analytical laboratory use — Specification and test methods
3 Terms and definitions
No terms and definitions are listed in this document.
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 https:// www .electropedia .org/
4 Principle
The water content of a sample of tobacco or a tobacco product is determined, using the volumetric
procedure, by extraction of water by shaking the sample with dry methanol, followed by injection of an
aliquot portion into the titration vessel, titration with pyridine-free Karl Fischer reagent and calculation
of the water content. The results are reported as mass percent (%).
If a size reduction (grinding or cutting) is applied, it can create a decrease in the original water content.
Cryogenic techniques may be used to prevent such moisture losses.
5 Reagents
Use only reagents of recognized analytical grade.
5.1 Karl Fischer reagent, free from pyridine, having a water equivalent per millilitre of reagent of
approximately 2 mg to 5 mg.
5.2 Methanol, with a water content of less than 0,05 g per 100 g.
Methanol is hygroscopic so it is recommended to cap the bottle with an automatic delivery pipette
equipped with drying tube.
WARNING — Methanol is toxic. There is danger of very serious irreversible effects through
inhalation, contact with the skin and if swallowed. Take precautions and read Material Safety
Data Sheets (MSDS).
5.3 Desiccant, silica gel, freshly activated.
5.4 Water, in accordance with grade 2 of ISO 3696, or better.
6 Apparatus
Usual laboratory apparatus and, in particular, the following items.
All glassware used in the preparation and in the water determination shall be heated at (105 ± 5) °C
for at least 1 h after visible water has evaporated. The glassware shall then be cooled and stored in a
desiccator over desiccant (5.3) until used.
6.1 Karl Fischer apparatus for automatic titration, consisting of items 6.1.1 to 6.1.5.
6.1.1 Apparatus for the detection of the titration end point, according to the biamperiometrical
method.
6.1.2 Double electrode, made of platinum.
6.1.3 Magnetic stirrer.
6.1.4 Titration vessel.
6.1.5 Automatic burettes, for methanol and Karl Fischer reagent.
6.2 Mechanical shaker, rotary platform, adjustable to a shaking frequency suitable for vigorous
mixing.
6.3 Microsyringe, for the determination of the water equivalent, of capacity 50 µl.
6.4 Glass volumetric pipettes, class A, of capacities 10 ml and 20 ml, in accordance with ISO 648.
6.5 Conical flasks, of capacities 250 ml and 500 ml, with a conical ground glass joint.
6.6 Hot-air oven, capable of maintaining a temperature of (105 ± 5) °C.
7 Standardization of the Karl Fischer reagent
Add sufficient methanol (5.2) to the titration vessel (6.1.4) to immerse the tips of the electrodes. Titrate
any residual solution (see NOTE) in the titration vessel to its end point by addition of Karl Fischer
reagent (5.1).
Add 50 µl of water to the titration vessel using the microsyringe (6.3). To ensure that the syringe does
not contain air bubbles, fill it to above the 50 µl mark, invert it and tap the air bubbles to the top. Then
depress the plunger to the 50 µl mark and remove excess water quickly from the needle tip with a
tissue. As an alternative, fill the syringe with 50 µl of water and weigh the syringe. After dosage, weigh
the syringe again and note the exact mass of water.
Transfer the 50 µl of water to the titration vessel, taking care to inject the water directly into the
solution, not allowing any to fall onto the neck or walls of the vessel. Where the vessel can be fitted with
a rubber membrane cap, this shall be used and the needle inserted through the cap. If a water droplet
remains on the needle tip, remove it by touching the surface of the solution in the vessel.
Titrate with Karl Fischer reagent (5.1) and record the titration value. Repeat the process. If the
difference between the values of two determinations is not greater than 0,05 ml, take the mean of two
determinations. Otherwise, repeat the whole determination.
Standardize the Karl Fischer reagent every working day.
For best results with the Karl Fischer technique, it is important to ensure that all stages of the analysis
are carried out in a uniform manner, extract to extract, sample to sample, day to day.
NOTE It is common practice with the direct titration technique to carry out a titration “on top” of residual
solution in the titration vessel, i.e. without removing the residual solution. When the volume in the vessel
reaches a certain level, the liquid is run to waste, retaining just enough for the electrode tips to be immersed.
In time, however, the methanol concentration in the vessel falls to a level such that the reaction cannot proceed
satisfactorily. A precipitate can form and false titration values can be obtained. Only experience will tell when
titration “on top of” residual solution has reached this point, and then the titration ve
...

INTERNATIONAL ISO
STANDARD 6488
Third edition
2021-06
Corrected version
2021-10
Tobacco and tobacco products —
Determination of water content —
Karl Fischer method
Tabac et produits du tabac — Détermination de la teneur en eau —
Méthode de Karl Fischer
Reference number
© ISO 2021
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus . 2
7 Standardization of the Karl Fischer reagent . 2
8 Sampling . 3
9 Procedure .3
9.1 Sample handling . 3
9.2 Test portion . 4
9.3 Preparation of titration apparatus . 4
9.4 Blank test . 4
9.5 Determination . 4
10 Expression of results . 5
11 Repeatability and reproducibility .5
12 Test report . 6
Bibliography . 8
iii
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 126, Tobacco and tobacco products.
This third edition cancels and replaces the second edition (ISO 6488:2004), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 6488:2004/Cor 1:2008.
The main changes compared to the previous edition are as follows:
— the term high-moisture tobacco has been deleted;
— further information on interlaboratory testing including additional sample types and corresponding
statistical data have been added.
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.
This corrected version of ISO 6488:2021 incorporates the following correction:
— a warning for the safe handling of methanol has been added in 5.2.
iv
Introduction
This document specifies a Karl Fischer method for the determination of the water content of tobacco
and tobacco products. Independent collaborative studies were conducted in 2002, 2009, and 2018. This
method is applicable to ground tobacco, a range of smokeless tobacco products, cigarette filler and
ground cigars.
v
INTERNATIONAL STANDARD ISO 6488:2021(E)
Tobacco and tobacco products — Determination of water
content — Karl Fischer method
1 Scope
This document specifies a method for the determination of water content by the Karl Fischer method. It
is applicable to raw tobacco as well as tobacco taken from finished products. The method is suitable for
water contents ranging from a mass fraction of at least 2 % to 55 %.
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 648, Laboratory glassware — Single-volume pipettes
ISO 3696, Water for analytical laboratory use — Specification and test methods
3 Terms and definitions
No terms and definitions are listed in this document.
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 https:// www .electropedia .org/
4 Principle
The water content of a sample of tobacco or a tobacco product is determined, using the volumetric
procedure, by extraction of water by shaking the sample with dry methanol, followed by injection of an
aliquot portion into the titration vessel, titration with pyridine-free Karl Fischer reagent and calculation
of the water content. The results are reported as mass percent (%).
If a size reduction (grinding or cutting) is applied, it can create a decrease in the original water content.
Cryogenic techniques may be used to prevent such moisture losses.
5 Reagents
Use only reagents of recognized analytical grade.
5.1 Karl Fischer reagent, free from pyridine, having a water equivalent per millilitre of reagent of
approximately 2 mg to 5 mg.
5.2 Methanol, with a water content of less than 0,05 g per 100 g.
Methanol is hygroscopic so it is recommended to cap the bottle with an automatic delivery pipette
equipped with drying tube.
WARNING — Methanol is toxic. There is danger of very serious irreversible effects through
inhalation, contact with the skin and if swallowed. Take precautions and read Material Safety
Data Sheets (MSDS).
5.3 Desiccant, silica gel, freshly activated.
5.4 Water, in accordance with grade 2 of ISO 3696, or better.
6 Apparatus
Usual laboratory apparatus and, in particular, the following items.
All glassware used in the preparation and in the water determination shall be heated at (105 ± 5) °C
for at least 1 h after visible water has evaporated. The glassware shall then be cooled and stored in a
desiccator over desiccant (5.3) until used.
6.1 Karl Fischer apparatus for automatic titration, consisting of items 6.1.1 to 6.1.5.
6.1.1 Apparatus for the detection of the titration end point, according to the biamperiometrical
method.
6.1.2 Double electrode, made of platinum.
6.1.3 Magnetic stirrer.
6.1.4 Titration vessel.
6.1.5 Automatic burettes, for methanol and Karl Fischer reagent.
6.2 Mechanical shaker, rotary platform, adjustable to a shaking frequency suitable for vigorous
mixing.
6.3 Microsyringe, for the determination of the water equivalent, of capacity 50 µl.
6.4 Glass volumetric pipettes, class A, of capacities 10 ml and 20 ml, in accordance with ISO 648.
6.5 Conical flasks, of capacities 250 ml and 500 ml, with a conical ground glass joint.
6.6 Hot-air oven, capable of maintaining a temperature of (105 ± 5) °C.
7 Standardization of the Karl Fischer reagent
Add sufficient methanol (5.2) to the titration vessel (6.1.4) to immerse the tips of the electrodes. Titrate
any residual solution (see NOTE) in the titration vessel to its end point by addition of Karl Fischer
reagent (5.1).
Add 50 µl of water to the titration vessel using the microsyringe (6.3). To ensure that the syringe does
not contain air bubbles, fill it to above the 50 µl mark, invert it and tap the air bubbles to the top. Then
depress the plunger to the 50 µl mark and remove excess water quickly from the needle tip with a
tissue. As an alternative, fill the syringe with 50 µl of water and weigh the syringe. After dosage, weigh
the syringe again and note the exact mass of water.
Transfer the 50 µl of water to the titration vessel, taking care to inject the water directly into the
solution, not allowing any to fall onto the neck or walls of the vessel. Where the vessel can be fitted with
a rubber membrane cap, this shall be used and the needle inserted through the cap. If a water droplet
remains on the needle tip, remove it by touching the surface of the solution in the vessel.
Titrate with Karl Fischer reagent (5.1) and record the titration value. Repeat the process. If the
difference between the values of two determinations is not greater than 0,05 ml, take the mean of two
determinations. Otherwise, repeat the whole determination.
Standardize the Karl Fischer reagent every working day.
For best results with the Karl Fischer technique, it is important to ensure that all stages of the analysis
are carried out in a uniform manner, extract to extract, sample to sample, day to day.
NOTE It is common practice with the direct titration technique to carry out a titration “on top” of residual
solution in the titration vessel, i.e. without removing the residual solution. When the volume in the vessel
reaches a certain level, the liquid is run to waste, retaining just enough for the electrode tips to be immersed.
In time, however, the methanol concentration in the vessel falls to a level such that the reaction cannot proceed
satisfactorily. A precipitate can form and false titration values can be obtained. Only experience will tell when
titration “on top of” residual solution has reached this point, and then the titration ve
...