ISO 10101-3:2022
(Main)Natural gas — Determination of water by the Karl Fischer method — Part 3: Coulometric procedure
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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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)
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© ISO 2022
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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
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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.
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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⋅
HO
2
m =
HO
2
zF⋅
where
z
is the number of exchanged electrons;
M the molecular weight of water;
HO
2
F
the Faraday constant (96 485 C/mol);
Q
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.
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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.
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INTERNATIONAL STANDARD I
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