Natural gas — Determination of water by the Karl Fischer method — Part 1: General requirements

This document specifies general requirements for the determination of water in natural gas using the Karl Fischer method (see Reference [1]). ISO 10101-2 and ISO 10101-3 specify two individual methods of determination, a titration procedure and a coulometric procedure, respectively.

Gaz naturel — Dosage de l'eau par la méthode de Karl Fischer — Partie 1: Exigences générales

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STANDARD 10101-1
Second edition
Natural gas — Determination of water
by the Karl Fischer method —
Part 1:
General requirements
Gaz naturel — Dosage de l'eau par la méthode de Karl Fischer —
Partie 1: Exigences générales
Reference number
ISO 10101-1:2022(E)
© ISO 2022

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ISO 10101-1:2022(E)
© ISO 2022
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  © ISO 2022 – All rights reserved

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ISO 10101-1:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
4.1 General . 1
4.2 Principle of the titration method . 1
4.3 Principle of the coulometric method . 2
5 Reactions and interferences .2
6 Sampling . 3
7 Measurement uncertainty .3
Bibliography . 4
© ISO 2022 – All rights reserved

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ISO 10101-1:2022(E)
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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 10101-1:1993), which has been technically
The main changes are as follows:
— Clause 2 and Bibliography were revised;
— New fixed structure numbering inserted.
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 10101-1:2022(E)
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 method for the determination of moisture has several practical advantages compared
to other methods for moisture determination, such as accuracy, speed and selectivity.
The Karl Fischer method is selective for water, because the titration reaction itself consumes water.
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.
KF titration is essentially based on the Bunsen reaction used for the determination of sulphur dioxide
in aqueous solution:
22 22 4
If an excess of sulphur dioxide with simultaneous neutralization of the sulphuric acid formed shift the
reaction equilibrium to the right, the Bunsen reaction can also be used for the determination of water.
Karl Fischer used pyridine as (neutralization) base, thus developing the classical KF reagent. This was
a solution of iodine and sulphur dioxide in a solvent mixture of pyridine and methanol . The fact that
the pyridine contained in the reagent has a strong unpleasant odour and toxicity and the reaction
runs stoichiometrically only within a certain pH range led to the revision of the KF reagents . Scholz
formulated the following KF reaction based on imidazole:
32 33
where RN = Base.
22 33 43
Volumetric KF titration is preferably used for the determination of large amounts of water in the range
of 1 mg to 100 mg

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