Natural gas — Determination of water by the Karl Fischer method — Part 3: Coulometric procedure

This document specifies a coulometric procedure for the determination of water content by the Karl Fischer method. The method is applicable to natural gas and other gases which do not react with Karl Fischer (KF) reagents. It applies to water concentrations between 5 mg/m3 and 5 000 mg/m3. Volumes are expressed at temperature of 273,15 K (0 °C) and a pressure of 101,325 kPa (1 atm).

Gaz naturel — Dosage de l'eau par la méthode de Karl Fischer — Partie 3: Méthode coulométrique

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Status
Published
Publication Date
30-Aug-2022
Current Stage
6060 - International Standard published
Due Date
03-Dec-2022
Completion Date
31-Aug-2022
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ISO 10101-3:2022 - Natural gas — Determination of water by the Karl Fischer method — Part 3: Coulometric procedure Released:31. 08. 2022
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INTERNATIONAL ISO
STANDARD 10101-3
Second edition
2022-08
Natural gas — Determination of water
by the Karl Fischer method —
Part 3:
Coulometric procedure
Gaz naturel — Dosage de l'eau par la méthode de Karl Fischer —
Partie 3: Méthode coulométrique
Reference number
ISO 10101-3:2022(E)
© ISO 2022
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ISO 10101-3:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

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

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© ISO 2022 – All rights reserved
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ISO 10101-3:2022(E)
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 Sampling ....................................................................................................................................................................................................................... 5

8 Procedure ....................................................................................................................................................................................................................6

8.1 Installation ................................................................................................................................................................................................. 6

8.2 Testing the response ......................................................................................................................................................................... 6

8.3 Measurement ........................................................................................................................................................................................... 6

8.4 Blank value determination .......................................................................................................................................................... 6

9 Expression of the results .............................................................................................................................................................................7

9.1 Method of calculation ....................................................................................................................................................................... 7

9.2 Measurement uncertainty ............................................................................................................................................................ 7

10 Test report .................................................................................................................................................................................................................. 8

Bibliography ................................................................................................................................................................................................................................ 9

iii
© ISO 2022 – All rights reserved
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ISO 10101-3:2022(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 193, Natural Gas, Subcommittee SC 1,

Analysis of natural gas, in collaboration with the European Committee for Standardization (CEN)

Technical Committee CEN/TC 238, Test gases, test pressures, appliance categories and gas appliance types,

in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

This second edition cancels and replaces the first edition (ISO 10101-3:1993), which has been technically

revised.
The main changes are as follows:
— Clause 2 and Bibliography were revised;
— new fixed structure numbering inserted;
— Subclause 9.2 Measurement of uncertainty was added.
A list of all parts in the ISO 10101 series can be found on the ISO website.
© ISO 2022 – All rights reserved
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ISO 10101-3:2022(E)
Introduction

Water vapour may be present in natural gas due to, for example, natural occurrence in the well

production stream, the storage of gas in underground reservoirs, transmission or distribution through

mains containing moisture or other reasons.

The Karl Fischer (KF) titration can be divided into two basic techniques – depending on the application

range – volumetric and coulometric KF titration. The two analysis techniques differ in the mode of

iodine addition or generation. Volumetric KF titration is preferably used for the determination of large

amounts of water in the range of 1 mg to 100 mg. Coulometry, however, is a micro-method which is

particularly well suited for determination of quantities of water from 10 μg to 10 mg.

Modern KF coulometers cover a range from 10 μg to 200 mg of water. Usually a resolution of 0,1 μg of

water is achieved.

In coulometric water determination, iodine is not added in the form of a titrating solution but rather

directly produced from an iodine-containing solution by an anodic oxidation reaction. The high analytic

precision at low absolute water quantities makes coulometric KF titration particularly well suited for

determination of the water content in aqueous gases.

Coulometric KF titration can be subdivided according to two distinct designs of the analysis cell:

Cells with and without diaphragm. In both variants, the measuring cells are made of a titration

vessel tightly sealed to prevent moisture ingress. The sample gas is passed directly through a glass

frit into the KF titration cell. Thus, absorption of moisture from the environment is prevented and the

gas finely dispersed. The fine distribution of the gas in the hygroscopic KF solution provides a large

surface for material exchange, so that the water contained in the gas can be fully absorbed by the

solution and then titrated. In the version with a diaphragm, the cell is divided into a large anode and

a small cathode compartment, each filled with different reagents. Spatial separation is achieved by

means of the diaphragm. In both compartments platinum electrodes are installed, via which a working

current is passed through the titration cell. Due to the applied current, at the anode iodine is formed,

which immediately reacts with the absorbed water from the gas sample. When all the water has been

consumed by the reaction, an excess of iodine is formed that will be detected voltametrically, ending

the titration. The amount of electricity consumed can be used to directly calculate, using Faraday’s law,

the quantity of water.
MQ⋅
m =
zF⋅
where
is the number of exchanged electrons;
M the molecular weight of water;
the Faraday constant (96 485 C/mol);
the charge which has flowed in C.

In the KF titration cell variant without a diaphragm there is no separation between the anode and

cathode chambers. Thus, for the filling of the cell only one reagent is needed and used. In order to prevent

direct reduction of iodine at the cathode, the cathode and anode are spatially separated from each other

by a large distance. The use of the cell without a diaphragm has the advantage that the titration cell is

easier to clean and only one reagent is consumed, whose replacement can be completely automated. In

addition, unlike in cells with a diaphragm, during longer downtimes no moisture can accumulate in the

diaphragm, making the titration cell faster to become operational. For the measurement of extremely

low water contents (few ppm of water), the leading KF equipment manufacturers recommend, despite

these advantages, use of a KF coulometer with diaphragm. For practical implementation, however, this

adds possible sources of error, complication and prolongation of the measurement times.

© ISO 2022 – All rights reserved
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ISO 10101-3:2022(E)

WARNING — Local safety regulations should be taken into account, when the equipment is located in

hazardous areas.
© ISO 2022 – All rights reserved
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INTERNATIONAL STANDARD I
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