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International
Standard
ISO 2620
First edition
Analysis of natural gas —
2024-03
Biomethane — Determination
of VOCs by thermal desorption
gas chromatography with
flame ionization and/or mass
spectrometry detectors
Analyse du gaz naturel — Biométhane — Détermination des
COV par chromatographie en phase gazeuse à désorption
thermique avec détecteurs à ionisation de flamme et/ou
spectrométrie de masse
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 1
5.1 Individual VOCs .1
5.2 Dilution solvent .2
5.3 Sorbents .2
6 Apparatus . 2
7 Preparation . 2
7.1 Field tube blanks.2
7.2 Solutions for liquid spiking .3
7.2.1 General .3
7.2.2 Solution containing approximately 0,2 mg/ml of each component .3
7.2.3 Solution containing approximately 0,04 mg/ml of each component .3
7.2.4 Solution containing approximately 0,01 mg/ml of each component .3
7.2.5 Standard tubes loaded with liquid spiking .3
8 Sampling . 3
9 Sample handling . 4
10 Procedure . 4
10.1 Desorption and analysis . .4
10.2 Quantification . . .6
10.3 Calculations .6
11 Quality assurance . 7
12 Test report . 7
Bibliography . 8
iii
Foreword
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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 408, Natural gas and biomethane for use in transport and biomethane for injection in the natural gas
grid, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
This document supports the implementation of specifications for biomethane and biogas when used in the
natural gas grids and when used as a transport fuel. Implementation of these specifications require fit-for-
purpose test methods with known performance and acceptable metrological traceability to support the
trade in renewable gases and conformity assessment.
Depending on the production method, biogas usually contains volatile organic compounds (VOCs) such as
terpenes, siloxanes, hydrocarbons, sulfur containing compounds, oxygenated hydrocarbons, halogenated
hydrocarbons, ketones, alcohols, and esters. VOCs can also be found in the biomethane even after upgrading.
v
International Standard ISO 2620:2024(en)
Analysis of natural gas — Biomethane — Determination of
VOCs by thermal desorption gas chromatography with flame
ionization and/or mass spectrometry detectors
1 Scope
This document describes a method for sampling and analysis of volatile organic compounds (VOCs),
including siloxanes, terpenes, organic sulfur compounds, in natural gas and biomethane matrices, using
thermal desorption gas chromatography with flame ionization and/or mass spectrometry detectors (TD-
GC-FID/MS).
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 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 terminology 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 sample gas is drawn through one sorbent tube where VOCs are retained while highly
volatile organic compounds as methane matrix gas pass through. Desorption of the tubes is then carried out
by thermal desorption (TD) in which the adsorbed substances are released with heat and then transferred
into a gas chromatograph (GC) equipped with a capillary column, a mass spectrometer (MS) and/or a flame
ionization detector (FID). MS data of the separated VOC components are compared with a mass spectral
library for compound identification. The use of the specific ions in addition to the retention time ensure
positive identification of a given VOC. Retention indices can also be used to identify peaks by comparing
measured retention indices with tabulated values. Quantification is performed using either the FID and/or
the MS detector. The expected quantification limit is (2-5) ng which is equivalent to (20-50) μg/m in the
sampled gas assuming a 100 ml gas sample volume.
5 Reagents and materials
5.1 Individual VOCs
For calibration purposes, purity > 99 %. Standard mixtures commercially available.
5.2 Dilution solvent
Dilution solvent of chromatographic quality, for preparing blend solutions for liquid spiking shall be free
from compounds of interest and compounds co-eluting with the compound(s) of interest (e.g. in methanol or
diethylether).
5.3 Sorbents
Sorbent are preconditioned and kept in a clean atmosphere.
EXAMPLE 2,6-diphenylphenylene oxide polymer.
Tubes compatible with the thermal desorption instrument to be used (6.8.3), typically containing 200 mg
sorbent, shall be sealed with for example screw-cap fittings with polytetrafluoroethylene.
The conditioning temperature shall not exceed the maximum rated temperature for the adsorbent resin.
The desorption tube shall preferably be conditioned 25 °C higher than the temperature at which it will be
desorbed.
6 Apparatus
6.1 Micro-syringe, 5 µl or 10 µl liquid syringe readable to 0,1 µl.
6.2 Gas-tight syringe, 100 ml readable to 5 ml, for indirect sampling.
6.3 Tubings, silicon-free and sulfur-free tubings.
6.4 Volumetric flask, in inert material, e.g. glass, quartz, polytetrafluoroethylene, 50 ml, class A.
6.5 Flowrate controller, volumetric, (50 to 500) ml/min readable to 2 ml/min.
6.6 Precision scale, 1 mg to 20 mg readable to 0,1 mg.
6.7 Sampling system, capable of accurately and precisely drawing natural gas or biomethane flow
through the sorbent tubes.
6.8 Gas chromatograph
6.8.1 Detectors, mass spectrometer in electron ionization (EI) mode and
...