Natural gas — Determination of water by the Karl Fischer method — Part 2: Volumetric procedure

This document specifies a volumetric procedure for the determination of water content in natural gas. Volumes are expressed in cubic metres at a temperature of 273,15 K (0 °C) and a pressure of 101,325 kPa (1 atm). It applies to water concentrations between 5 mg/m3 and 5 000 mg/m3.

Gaz naturel — Dosage de l'eau par la méthode de Karl Fischer — Partie 2: Méthode volumétrique

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STANDARD 10101-2
Second edition
Natural gas — Determination of water
by the Karl Fischer method —
Part 2:
Volumetric procedure
Gaz naturel — Dosage de l'eau par la méthode de Karl Fischer —
Partie 2: Méthode volumétrique
Reference number
ISO 10101-2:2022(E)
© ISO 2022

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ISO 10101-2:2022(E)
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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  © ISO 2022 – All rights reserved

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ISO 10101-2:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 2
6 Apparatus . 3
7 Determination of the water equivalent of the Karl Fischer reagent .3
8 Sampling . 4
9 Procedure .4
10 Expression of results . 6
10.1 Method of calculation . 6
10.2 Measurement uncertainty . 6
11 Test report . 6
Annex A (informative) Karl Fischer apparatus . 8
Bibliography .11
© ISO 2022 – All rights reserved

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ISO 10101-2:2022(E)
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
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committee has been established has the right to be represented on that committee. International
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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
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
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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
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 10101-2:1993), which has been technically
The main changes are as follows:
— Clause 2 and Bibliography were revised;
— New fixed structure numbering inserted;
— Clause 5 was modified;
— Clause 9 was modified;
— 10.2 was modified.
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 10101-2:2022(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.
© ISO 2022 – All rights reserved

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Natural gas — Determination of water by the Karl Fischer
method —
Part 2:
Volumetric procedure
WARNING — Local safety regulations should be taken into account, when the equipment is located in
hazardous areas.
1 Scope
This document specifies a volumetric procedure for the determination of water content in natural gas.
Volumes are expressed in cubic metres at a temperature of 273,15 K (0 °C) and a pressure of 101,325 kPa
3 3
(1 atm). It applies to water concentrations between 5 mg/m and 5 000 mg/m .
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 383, Laboratory glassware — Interchangeable conical ground joints
ISO 10101-1, Natural gas- Determination of water by the Karl Fischer method – Part 1- Introduction
ISO 14532, Natural gas — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14532 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 https:// www .electropedia .org/
4 Principle
A measured volume of gas is passed through a cell containing a relatively small volume of absorbent
solution. Water in the gas is extracted by the absorbent solution and subsequently titrated with
Karl Fischer reagent. The design of the cell and the absorbent solution are chosen to ensure efficient
collection of the water at the high flowrates necessary.
The principle and chemical reactions of the Karl Fischer method are given in ISO 10101-1:2020, Clauses 4
and 5; interferences are also described in ISO 10101-1:2020, Clause 5.
ISO 10101-1:2020, Clause 5 describes interfering substances which may be present in natural gas and
corrections for the interference of hydrogen sulfide and mercaptans.
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ISO 10101-2:2022(E)
5 Reagents
5.1 Karl Fischer reagent, of which the water equivalent is approximately 5 mg/ml.
NOTE For most applications, commercially available Karl Fischer (KF) reagent with a water equivalent of
approximately 5 mg/ml has been found adequate.
The reagent can be bought as a one-component reagent, which contains all the necessary reagents
(iodine, sulfur dioxide and the base (e.g. imidazole)) dissolved in an anhydrous solvent (methanol or
2-methoxyethanol) or it can be provided as two-component reagent, i.e. a solvent reagent and a titrant
reagent which are mixed before use.
The solvent reagent contains sulfur dioxide and a base (e.g. an alkali or alkaline earth metal benzoate,
ammonia, imidazole). The titrant reagent contains iodine. The two-component reagent provides a stable
titre as long as any moisture is prevented from entering into the reagents and a better shelf life.
If required, it may be prepared following the procedure in 5.1.1.
5.1.1 Preparation of Karl Fischer reagent Components Methanol, with a water content of less than 0,01 % (mass fraction). Use commercially
available dry methanol, anhydrificated in the lab by one of the following procedures Place 2 l of methanol in a two-neck 3 l flask and add 10 g of magnesium turnings. Add a
crystal of iodine, connect the flask to a reflux condenser and leave overnight. Next day, add a further
5 g of magnesium turnings and reflux for 1 h. Connect the top of the reflux condenser to a still head,
a double surface condenser and a collection flask. Disconnect the water flow through the condenser
originally used for reflux and distil the contents of the flask. Discard the first 150 ml of condensate.
Distil the rest into dried 1 litre flasks. Vent the system through a drying tube during distillation. Dry the methanol over a freshly activated molecular sieve. 2-Methoxyethanol, with a water content of less than 0,01 % (mass fraction).
NOTE This can be used as an alternative to methanol ( with a lower vapour pressure and therefore
less losses due to evaporation during sampling of the gas Imidazol, anhydrous. Sulfur dioxide, liquefied and dry. Iodine. Preparation
Measure 300 ml of dry methanol ( or 2-methoxyethanol ( and 110 ml of anhydrous
imidazole ( into a 750 ml conical flask. Slowly pass liquid sulfur dioxide ( into this
solution, mixing carefully until the increase in weight is 43 g. Cool this solution in a freezing mixture.
When cool, add sufficient iodine ( to give a permanent light brown colour. Then add 63 g of
iodine and swirl until dissolved. Make up to 500 ml with dry methanol or 2-methoxyethanol. Leave
standing in the stoppered conical flask for 24 h before use. Commercial reagents, when aged, may give a
slow response near the end point.
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ISO 10101-2:2022(E)
5.2 Absorbent solution.
5.2.1 Components Ethylene glycol, with a water content less than 0,1 % (mass fraction). Sulfur dioxide, liquefied and dry. Imidazol, anhydrous Karl Fischer reagent (see 5.1).
5.2.2 Preparation of the absorbent solution
Slowly add 20 g of sulfur dioxide ( to 180 ml of anhydrous imidazole (, while mixing
carefully (solution A).
To prepare the absorbent solution, add 55 ml of dry ethylene glycol (, 55 ml of Karl Fischer
reagent ( and 73 ml of solution A to a round bottomed flask. Boil under reflux for 10 min with a
drying tube on the condenser, and then cool.
5.3 Reference solution, e.g. water and methanol mixture, with a water content of 5,0 mg/l ± 0,2 mg
or 10,0 mg/l ± 0,4 g. Keep this solution in a flask sealed with a septum.
NOTE There are reference solutions commercially available. They consist of stable solvent mixtures with
specific composition and precisely determined water content, supplied in airtight glass ampoules to ensure
quality when opened by the end user. The exact amount of water is given on the certificate of analysis. Typically,
the reference solutions are filled under Argon in 4 ml or 8 ml glass ampoules.
6 Apparatus
6.1 Karl Fischer apparatus, as described in Anne

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