Natural gas - Extended analysis - Gas-chromatographic method (ISO 6975:1997)

describes the method of test to determine the stability of transmission performance of a finished cable used in analogue and digital communication systems when submitted to temperature changes which may occur during use, storage or transportation.

Erdgas - Erweiterte Analyse - Gaschromatographisches Verfahren (ISO 6975:1997)

Diese Internationale Norm beschreibt die Anforderungen für die quantitative Analyse der folgenden Erdgaskomponenten:
Helium
Wasserstoff
Argon
Sauerstoff
Stickstoff
Kohlenstoffdioxid
gesättigte Kohlenwasserstoffe von C1 bis C5
Kohlenwasserstofffraktionen ab C6 aufwärts
aromatische Verbindungen wie Benzol und Toluol.
Die gaschromatographischen Verfahren bestimmen diese Komponenten in den folgenden Gehaltsbereichen:
Sauerstoff:   0,001 % (n/n)   bis   0,5 % (n/n)
Helium:   0,001 % (n/n)   bis   0,5 % (n/n)
Wasserstoff:   0,001 % (n/n)   bis   0,5 % (n/n)
Argon:   0,001 % (n/n)   bis   0,5 % (n/n)
Stickstoff:   0,001 % (n/n)   bis   40 % (n/n)
Kohlenstoffdioxid:   0,001 % (n/n)   bis   40 % (n/n)
Methan:   0,001 % (n/n)   bis   100 % (n/n)
Ethan:   0,02 % (n/n)   bis   15 % (n/n)
Propan:   0,001 % (n/n)   bis   5 % (n/n)
höhere Kohlenwasserstoffe:   Das Verfahren kann Kohlenwasserstoffkomponenten ab einer Konzentration von 10-6 (n/n) bis zur jeweiligen Maximalkonzentration messen, was mit der Anforderung in Einklang steht, dass das Gas bei beliebigem Druck im Bereich zwischen 1 ´ 102 kPa und 7 ´ 103 kPa frei von Kohlenwasserstoffkondensaten ist.
Dieses Verfahren ist nicht dazu ausgelegt, Sauerstoff- (Wasserdampf, Methanol, Glykole) und Schwefelverbindungen zu bestimmen.
Die Möglichkeit zur eindeutigen Identifizierung von Kohlenwasserstoffen oberhalb C6 ist nicht gegeben. Selbst wenn durch das "Spiking" eines Gases mit bekannten Komponenten aufgezeigt werden kann, an welcher Stelle deren Elution stattfindet, kann nicht mit Sicherheit behauptet werden, dass diese Komponente die einzige mit der jeweils in Rede stehenden Retentionszeit ist. Nicht identifizierte Komponenten werden entsprechend jener Kohlenstoffzahl klassifiziert, die aufgrund der Analyse als angemessen anzusehen ist. Dies stellt zwar eine notwendige Vereinfachung dar, erlaubt jedoch die Gewinnung vernünftiger quantitativer Werte.
Dieses Verfahren ist für den Einsatz in Fällen vorgesehen, in denen eine Analyse der Hexane und höheren Kohlenwa

Gaz naturel - Analyse étendue - Méthode par chromatographie en phase gazeuse (ISO 6975:1997)

La présente Norme internationale fixe les spécifications relatives à l'analyse quantitative des constituants suivants du gaz naturel:
  hélium
  hydrogène
  argon
  oxygène
  azote
  dioxyde de carbone
  hydrocarbures saturés de C1 à C5
  fractions d'hydrocarbures, C6 et supérieurs
  composés aromatiques tels que le benzène et le toluène
Les méthodes de chromatographie en phase gazeuse permettent de déterminer
  les constituants dans les gammes suivantes:
  oxygène: 0,001 % (n/n) à 0,5 % (n/n)
  hélium: 0,001 % (n/n) à 0,5 % (n/n)
  hydrogène: 0,001 % (n/n) à 0,5 % (n/n)
  argon: 0,001 % (n/n) à 0,5 % (n/n)
  azote: 0,001 % (n/n) à 40 % (n/n)
  dioxyde de carbone: 0,001 % (n/n) à 40 % (n/n)
  méthane: 50 % (n/n) à 100 % (n/n)
  éthane: 0,02 % (n/n) à 15 % (n/n)
  propane: 0,001 % (n/n) à 5 % (n/n)
  hydrocarbures supérieurs: la méthode peut mesurer les constituants
    depuis 10-6 (n/n) jusqu'à leur concentration maximale compatible
    avec la prescription selon laquelle le gaz ne doit contenir aucun condensat
    d'hydrocarbure, à n'importe quelle pression, dans la gamme 1 x 102
    kPa à 7 x 103 kPa.
Cette méthode n'est pas destinée à identifier les composés
oxygénés (la vapeur d'eau, le méthanol, les glycols) et les
composés sulfurés. Il est impossible que l'identification des hydrocarbures
supérieurs à C6 soit ambiguë. Même lorsqu'un
pic indique le point d'élution des constituants connus d'un mélange
gazeux, on ne peut pas établir avec certitude que ce constituant est le
seul qui présente ce temps de rétention. Les constituants non identifiés
sont classés selon l'indice de carbone qui est apparu approprié
suite à l'analyse. Bien que cette simplification soit nécessaire,
elle permet d'obtenir une valeur quantitative convenable. Cette méthode
est à utiliser lorsqu'on désire analyser la composition des hexanes+
et/ou effectuer une analyse
complète.
La méthode n'est pas destinée à des gaz en phase dense dont
la pression dépasse le cricondebar (pression de condensation critique)
ou, pour des échantillons de gaz ne contenant aucun condensat d'hydrocarbures
en quantité mesurable, de l'eau à I'état liquide ou de fluide
de traitement comme le méthanol ou les glycols (voir ISO 6570-1 et ISO
10715).
II est peu vraisemblable que les gaz traités en vue de leur transport contiennent
une proportion décelable d'hydrocarbures supérieurs à C12.
Les échantillons prélevés plus près de la tête
de puits peuvent contenir, avant leur passage par l'usine de traitement, des hydrocarbures
allant jusqu'a cl6 ou au-delà.

Zemeljski plin – Širše analize – Plinsko-kromatografska metoda (ISO 6975:1997)

General Information

Status
Published
Publication Date
30-Jun-2005
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Jul-2005
Due Date
01-Jul-2005
Completion Date
01-Jul-2005

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SLOVENSKI STANDARD
SIST EN ISO 6975:2005
01-julij-2005
Zemeljski plin – Širše analize – Plinsko-kromatografska metoda (ISO 6975:1997)
Natural gas - Extended analysis - Gas-chromatographic method (ISO 6975:1997)
Erdgas - Erweiterte Analyse - Gaschromatographisches Verfahren (ISO 6975:1997)
Gaz naturel - Analyse étendue - Méthode par chromatographie en phase gazeuse (ISO
6975:1997)
Ta slovenski standard je istoveten z: EN ISO 6975:2005
ICS:
75.060 Zemeljski plin Natural gas
SIST EN ISO 6975:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 6975:2005

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SIST EN ISO 6975:2005
EUROPEAN STANDARD
EN ISO 6975
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2005
ICS 75.060
English version
Natural gas - Extended analysis - Gas-chromatographic method
(ISO 6975:1997)
Gaz naturel - Analyse étendue - Méthode par Erdgas - Erweiterte Analyse - Gaschromatographisches
chromatographie en phase gazeuse (ISO 6975:1997) Verfahren (ISO 6975:1997)
This European Standard was approved by CEN on 17 April 2005.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6975:2005: E
worldwide for CEN national Members.

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SIST EN ISO 6975:2005
EN ISO 6975:2005 (E)






Foreword



The text of ISO 6975:1997 has been prepared by Technical Committee ISO/TC 193 "Natural
gas” of the International Organization for Standardization (ISO) and has been taken over as EN
ISO 6975:2005 by CMC.

This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by November 2005, and conflicting national
standards shall be withdrawn at the latest by November 2005.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.



Endorsement notice

The text of ISO 6975:1997 has been approved by CEN as EN ISO 6975:2005 without any
modifications.

2

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SIST EN ISO 6975:2005
INTERNATIONAL
STANDARD
Second edition
1997-04-O 1
- Extended analysis -
Natural gas
Gas-chromatographic method
M&hode par chromatographie
Gaz nature/ - Analyse &endue -
en phase gazeuse
Reference number
IS0 69759 997(E)

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SIST EN ISO 6975:2005
IS0 6975:1997(E)
Page
Contents
1
..........................................................................................
1 Scope
2
.................................................................
2 Normative references
3
..................................................................................
3 Definitions
4
......................................................................................
4 Principle
......................................... 5
5 Analysis and analytical requirements
7
.................................................................................
6 Procedures
8
.....................................................
7 Calibration and control charts
11
................................................................................
8 Calculations
13
.....................................................................................
9 Precision
14
10 Test report .
Annexes
A Determination of the response curves for the main components
................................................................................. 15
in a sample
........................ 21
B Further details on the matrices used in annex A
22
List of retention indices .
C
24
D Bibliography .
0 IS0 1997
All rights reserved. Unless otherwise specified, no part of this publication may be
reproduced or utilized in any form or by any means, electronic or mechanical, including
photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Internet central@iso.ch
x.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
II

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SIST EN ISO 6975:2005
@ IS0 IS0 6975:1997(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
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. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard IS0 6975 was prepared by Technical Committee
ISO/TC 193, Natural gas, Subcommittee SC 1, Analysis of natural gas.
This second edition cancels and replaces the first edition (IS0 6975:1986),
which has been technically revised.
Annexes A to D of this International Standard are for information only.

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SIST EN ISO 6975:2005
@ IS0
IS0 6975:1997(E)
Introduction
This International that an accurate
Standa rd d escribes th e specifications
method for the co #mplete and extended a nalysis of natura I gas shall fulfil.
The analytical methods involve injection of natural gas on to packed or
open tubular (capillary) columns in one or more gas chromatographs. The
components coming off the columns are detected by thermal-conductivity
detector (TCD) or flame ionization detector (FID).
Compared to other analytical methods, the extended gas-chromatographic
analysis supplies considerable knowledge of the individual components in
the natural-gas mixture. This allows quantitative measurement of particular
components in the Cs+ fraction and calculation of physical properties.
Although the higher hydrocarbons influence physical properties such as
calorific values and density by less than 0,3 % and 0,004 %, respectively,
knowledge of them is required for evaluation of the pseudo-values for the
Cg+ fraction.
In addition, vapour phase equilibrium calculations often require detailed
composition data, especially of hydrocarbons with carbon numbers higher
than 6.
The simultaneous determination of benzene and other aromatics is needed
for gas consumers using natural gas as a chemical feedstock since these
components can interfere in some processes.
iv

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SIST EN ISO 6975:2005
IS0 6975:1997(E)
INTERNATIONAL STANDARD @ IS0
Extended analysis - Gas-chromatographic
Natural gas -
method
1 Scope
This International Standard describes the specifications for the quantitative analysis of the following components of
natural gas:
helium
hydrogen
argon
oxygen
nitrogen
carbon dioxide
saturated hydrocarbons from C1 to C5
hydrocarbon fractions from C6 upwards
aromatic compounds as benzene and toluene
The gas-chromatographic methods determine the components in the following ranges:
oxygen: 0,001 % (n/n) to 0,5 % (n/n)
to 0,5 % (n/n)
helium: 0,001 % (n/n)
hydrogen: 0,001 % (n/n) to 0,5 % (n/n)
argon: 0,001 % (n/n) to 0,5 % (n/n)
nitrogen: 0,001 % (n/n) to 40 % (n/n)
carbon dioxide: 0,001 % (n/n) to 40 % (n/n)
methane: 50 % (n/n) t0 100 % (n/n)
0,OZ % (n/n) t0 15 % (n/n)
ethane:
propane: 0,001 % (n/n) t0 5 % (n/n)
higher hydrocarbons: The method can measure hydrocarbon components from IO-6 (n/n) up to their
maximum concentration, which is compatible with the requirement that the gas is
free from hydrocarbon condensate at any pressure in the range 1 x IO* kPa to
7 x 103 kPa.
1

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SIST EN ISO 6975:2005
@ IS0
IS0 6975:1997(E)
This method is not intended for the determination of oxygen compounds (water vapour, methanol, glycols) or sulfur
compounds”
It is not possible to make unambiguous identifications of hydrocarbons above Ca. Even where “spiking” a gas
mixture with known components shows where they elute, it cannot be stated with certainty that such a
component is the only one with that retention time. Unidentified components are classified according to the carbon
number which the analysis indicates to be appropriate. While this is a necessary simplification, it does allow a
reasonable quantitative value to be obtained.
This method is intended for use in situations where the hexanes plus compositional breakdown and/or the
complete analysis is desired.
The method is not intended for dense phase gases whose pressure exceeds the cricondebar (critical condensation
pressure), or for gas samples containing any measurable hydrocarbon condensate, liquid water or process fluid
such as methanol or glycols (see IS0 6570-I and IS0 10715).
Gases which have been treated for transmission are unlikely to contain detectable levels of hydrocarbons above
C12. Samples taken from nearer the well head, before the gas has reached gas treatment plants, may contain
hydrocarbons to C16 or above.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this
International Standard. At the time of publication, the editions indicated were valid. All standards are subject to
revision, and parties to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain
registers of currently valid International Standards.
IS0 5725-l :I 994, Accuracy (trueness and precision) of measurement methods and results - Part I: General
principles and definitions.
IS0 6142:1981, Gas analysis - Preparation of calibration gas mixtures - Weighing methods.
Determination of composition of calibration gas mixtures - Comparison methods.
IS0 6143:1981, Gas analysis -
Determination of sulfur compounds - Part 1: General introduction.
IS0 6326-l : 1989, Natural gas -
Determination of sulfur compounds in natural gas - Part 2: Gas chromatographic
IS0 6326-2:1981, Gas analysis -
method using an electrochemical detector for the determination of odoriferous sulfur compounds.
IS0 6326-3:1989, Natural gas - Determination of sulfur compounds - Part 3: Determination of hydrogen sulfide,
mercaptan sulfur and carbon yi sulfide sulfur by potentiometry.
IS0 6326-4: 1994, Natural gas - Determination of sulfur compounds - Part 4: Gas chromatographic method using
a flame photometric detector for the determination of hydrogen sulfide, carbonyl sulfide and sulfur-containing
odoran ts.
I SO 6326-5: 1989, Natural gas - Determination of sulfur compounds - Part 5: Lingener combustion method.
IS0 6570-I :I 983, Natural gas - Determination of potential hydrocarbon liquid con tent - Part I: Principles and
general requirements.
IS0 6974-l :- 1), Natural gas - Determination of composition with defined uncertainty
chromatography -
bY gas
Part 7: Guidelines for tailored analysis.
1) To be published. (Revision, in parts, of IS0 6974:1984)
2

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SIST EN ISO 6975:2005
0 IS0 IS0 6975:1997(E)
IS0 6974-2: --*I, Natural gas - Determination of composition with defined uncertainty by gas chromatography -
Part 2: Measuring sys tern characteris tics and statistics for data treatment.
IS0 6974-3:
- 21, Natural gas - Determination of composition with defined uncertainty by gas chromatography -
Part 3: Determination of hydrogen, helium, inert gases and hydrocarbons up to Cs.
I SO 6974-4: - Determination of composition with defined uncertainty by gas chromatography -
- 21, Natural gas
Part 4: Determination of nitrogen, carbon dioxide and hydrocarbons (C, up to Cs and C6+) for a laboratory and
on-line measuring system.
- Determination of composition with defined uncertainty by gas chromatography -
IS0 6974-5: - 21, Natural gas
Part 5: Determination of nitrogen, carbon dioxide and hydrocarbons (Cl up to Cs and C,+, for a laboratory and
on-line process application.
I SO 107 15: 1997, Natural gas - Sampling guidelines.
Guidelines for traceability in analysis.
IS0 14111: 1997, Natural gas -
3 Definitions
For the purposes of this International Standard, the following definitions apply.
31 q resolution: Gas-chromatographic resolution is a characteristic of the separation of two adjacent peaks and is
- .
measured as twice the distance between the maxima of the named peaks divided by the sum of the intercepts on
the baseline made by tangents drawn to the peaks at half their height (see figure 1). The resolution RAB may be
expressed by the following equation:
&(B) - d&V
RAB =2x
w(B) + 4A)
where
d,(A) and dR(B) are the retention distances of the eluted components A and B;
w(A) and w(B) are the widths of the respective peaks at their base.
3.2 main components: The nitrogen, carbon dioxide and saturated hydrocarbons from methane to rt-pentane
present in a natural-gas sample.
3.3 associated components: The helium, hydrogen, argon and oxygen present in a natural-gas sample.
3.4 trace components: The hydrocarbons and/or groups of hydrocarbons from n-pentane upwards present in a
natural-gas sample.
3.5 other components: Those components for which this method is not intended, such as oxygen compounds
(water vapour, methanol, glycol) and sulfur compounds.
response: The response is the output signal for a component that is measured as peak area or peak height
3.6
(more often as peak area).
2) To be published. (Revision, in parts, of IS0 6974:1984)
3

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SIST EN ISO 6975:2005
IS0 6975:1997(E)
- Resolution of two adjacent peaks
Figure 1
37 reference component: The component present in th e working-reference ga sm ixture against which the
n the working-reference
relati ve respons #e factors of sample components not present i mixture are defined.
gas
3.8
relative response factor (for an FID): The relative response factor Ki is calculated as the ratio of the carbon
number of the reference component to the carbon number of a particular sample component. Thus if the reference
component is n-butane, then the relative response factor for C7 components in the sample (heptane isomers,
methylcyclohexane, toluene, etc.) is calculated as
4
=-=0,571
4
7
3.9 concentration of a group of components: The concentration of a group of components is the sum of the
concentrations of the normal hydrocarbon components and their isomers. The response of the group is the sum of
the responses of these components. The relative response of the group is equal to the relative response of the
normal alkane of the group. The group is named according to the normal alkane of the group.
4 Principle
The onents to be determined in a gaseous sample are physically separated by gas chromatography and
camp
corn pared with calibratio n data obtained under the same set of conditions.
The main components are separated using a packed or open tubular column in a gas chromatograph and detected
by TCD. An FID may be used additionally.
The analytical system used separates oxygen from nitrogen to check air contamination in the sample.
The hydrocarbons from propane upwards are separated using an open tubular column in a gas chromatograph and
detected by FID. The method assumes that the response of an FID to hydrocarbons is proportional to the carbon
number. Hence, components not present in the calibration gas are quantified by means of knowledge of their
carbon number.
Associated components can be determined by following special gas-chromatographic techniques (see e.g. the
various parts of IS0 6974).
4

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SIST EN ISO 6975:2005
@ IS0 IS0 6975:1997(E
Rli of a
ldentifica tion of hydrocarbons is by linear retention index calculation. The retention index component
is calcula ted as
Rli =1()0x ti-tx
4- 100x
qx + 1) - tx
where
is the retention time of component i;
4
is the retention time of an appropriate n-alkane of carbon number X;
tX
tix + 1) is the retention time of an n-alkane of carbon number (X + 1).
This method of calculation was described by Hayes and Pitzer[31 (see annex D) and is true only for temperature-
programmed analysis.
A list of retention indices is given in annex C.
The retention indices should be seen as indications rather than definite values. They are more valuable in indicating
the difference A(RI) between compounds.
5 Analysis and analytical requirements
5.1 Apparatus and materials
5.1.1 Analytical system
The analytical system shall consist of a gas-chromatographic unit and an integrator and data reduction system.
The gas-chromatographic unit may consist of one or more gas chromatographs capable of isothermal and/or
temperature-programmed operation and equipped with a TCD and/or an FID and a sample transfer and introduction
system.
Each gas chromatograph shall be connected to an integrator.
5.1.2 Reference gas mixtures
5.1.2.1 Certified-reference gas mixtures (CRMs)
Certified-reference gas mixtures are used for the determination of the response curves of the measuring system.
CRMs can be binary or multicomponent mixtures and shall be prepared gravimetrically in accordance with
IS0 6142 or certified and validated by comparison with primary-standard gas mixtures (PSMs) of closely related
composition (see IS0 6143).
The composition of the CRM shall be traceable to the composition of the PSM whenever available (see IS0 I41 11).
In the hierarchy of reference materials, this type of gas mixture corresponds to the certified reference material.
5.1.2.2 Working-reference gas mixtures (WRMs)
These mixtures are used as working standards for the regular calibration of the measuring system. WRMs can be
binary or multicomponent mixtures and shall be prepared gravimetrically in accordance with IS0 6142 or certified
and validated by comparison with CRMs of closely related composition (see IS0 6143).
The composition of the WRM shall be traceable to the composition of the PSM whenever available (see
IS0 14111).
5

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SIST EN ISO 6975:2005
@ IS0
IS0 6975:1997(E)
The concentration of trace components will be calculated with the aid of a reference component, so the WRM
need only contain main components.
For the determination of the main components, a WRM containing nitrogen, carbon dioxide and normal
hydrocarbons from methane to n-butane as a minimum is required. A second WRM containing helium, argon,
hydrogen and oxygen is also required for the determination of the associated components. In both mixtures,
methane shall be the complementary gas.
Optionally, a single gas mixture containing all the above-mentioned components can be used.
For safety reasons, regulations may require that a WRM containing oxygen be prepared with an inert
complementary gas.
The concentration of each component in the WRM shall be within the tolerances given in table 1 relative to those
expected in the sample gas.
- Tolerance between concentrations of components
Table 1
in the WRM and sample
I
Actual component concentration Derivation of component
concentration in WRM
in sample
% (n/n) (% relative to sample concentration)
up to 0,l Ik 100
+ 50
0,l to 1
1 to10 &IO
10 to 50 +5
50 to 100 +3
/
5.1.2.3 Control gas
A control gas is a high-pressure gas mixture of known composition containing all the components present in the
working-reference gas mixture. A control gas can be either a sample gas with a composition determined in
accordance with IS0 6143 or a multicomponent mixture prepared in accordance with IS0 6142.
A control gas is used for the determination of the mean (p) and standard deviation (a) of the concentrations of the
components detected.
5.2 Structure of the analysis
The analysis takes into account the following components:
.
main and associated components determined by using response curves, single-point calibration or a
xmc.
reference component;
trace components determined by using a reference component;
Xbc:
other components that are measured by using other methodologies (see e.g. the various parts of
xoc:
IS0 6326).
The summation of the concentrations, in % (n/n), is defined as 100:
6

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SIST EN ISO 6975:2005
IS0 6975:1997(E)
0 IS0
5.3 Resolution
5.3.1 Main components
The resolution between two adjacent peaks for each component from nitrogen to 2-methylpropane shall not be
less than 2.
The resolution between two adjacent peaks for each component from 2-methylpropane to n-pentane shall not be
less than 4.
In the event that a valve switching is performed in multicolumn analysis, the resolution between the peak of the
component eluted before switching the valve and the peak of the component that would be eluted without the
valve switching shall not be less than 4.
As oxygen is detected only to check air contamination of the sample gas, the resolution between the peaks of
oxygen and nitrogen shall not be less than 1,5.
5.3.2 Trace components
The column used for trace components shall also be capable of separating some of the main components,
i.e. hydrocarbons from C3 to Cg.
clopara ffins, the column shall be capable of the
To achieve satisfactory separation of light aromatics and cy
foll owing resolution:
the heig ht of the vail ey between et hane and propane shall not be
The ratio of the height of the ethane peak to
less than 1 5OO:l. For this measurement, the sample shall con tain approximately 3 % (n/n) of ethan e.
The resolution between 2-methylpropane and n-butane shall not be less than 4.
The resolution between n-pentane and n-hexane shall not be less than 15.
The resolution between n-octane and n-nonane shall not be less than 30.
NOTE - If such measurements are made from recorder charts, different conditions from those normally chosen to display
the chromatogram will be necessary. Thus two analyses at very different attenuations will be needed to measure the valley
between ethane and propane and the peak height of ethane.
5.3.3 Associated components
The resolution between two adjacent peaks shall not be less than 1,5.
6 Procedures
6.1 Setting up the analytical system
Set up all the ana lytical system in accordance with the manufacturer ’s instructions and the analytical
methods
chosen
The sample cylinder and transfer line shall be heated sufficiently to avoid condensation and sorption of higher
hydrocarbons in the sampling system. The sample cylinder and transfer line shall be heated to at least 10 K above
the sampling temperature. Special precautions shall be taken at any spot in the system where pressure reduction
occurs
NOTE - The temperature of a natural gas will drop by approximately 0,005 K per kilopascal of pressure reduction.

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SIST EN ISO 6975:2005
@ IS0
IS0 6975:1997(E)
6.2 Injection
Purge the sample valve slowly with the gas to be analysed, using at least 20 times the volume of the valve and
associated pipework.
Stop the purge to allow the gas to reach the temperature of the valve and ambient pressure, then inject. The
working-reference gas mixture shall be injected in the same way.
NOTE -
It is also possible to introduce the sample into a previously evacuated sample loop and allow it to equilibrate to
ambient pressure before injection.
7 Calibration and control charts
7.1 Calibration
Main components, except C, and C, hydrocarbons, shall be analysed using multi-level calibration.
C4 and C5 hydrocarbons can be analysed either using single-point calibration or using relative FID response factors.
Trace components shall be analysed using relative FID response factors. The concentration of the reference
component shall be less than 1 % (I&Z).
Associated components shall be analysed using single-point calibration.
7.1 .I Multi-level calibration (determination of response curve)
With multi-level calibration, the response curve for the detector over the range to be analysed is determined. This is
done with at least seven calibration points for each component, distributed equally over the range. These seven
points shall be determined using at least seven certified-reference gas mixtures as described in 5.1.2.1.
The response curve can be determined for each component as described in annex A.
NOTES
Using seven calibration points for each component enab Iles fourth -order detector behaviour to be confirmed with a high
ly indicates a defe ct ive detector.
se nsitivity. Third-order beha viour most
2 When determining a multi-level response curve, it is preferable that the ambient pressure is constant for the whole of the
calibration cycle since the amount injected is directly proportional to the ambient pressure. One way of avoiding problems is to
record the ambient pressure at each injection of calibration gas and then correct the measured response to standard pressure
using the following equation:
-R,xI/S’
R
c,st -
PC
where
R cst is the response corrected to standard pressure;
is the measured response;
Rc8
is the ambient pressure, in kilopascals;
PC
pst is standard atmospheric pressure (I 01,325 kPa).
7.12 Single-point calibration (determination of response curve)
Single-point calibration is used on the assumption that the detector behaviour intercepts the origin and is linear over
a small range around the point at which the chromatograph is calibrated.
8

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SIST EN ISO 6975:2005
@ IS0 IS0 6975:1997(E)
7.2 Regular calibration
Carry out regular calibration using a WRM as described in 5.1.2.2. Do this by injecting, in accordance with the
procedures given in 6.2, the WRM twice and taking the mean result to adjust the response curve.
For the calibration interval, see 7.3.
7.3 Control charts
Inspection of the calibration data (see 7.1 and 7.2) can give an indication as to whether the equipment and the
method is working satisfactorily. However, the determination of the response curve is intended to define
the instrument response to the components present in the WRM, and it is therefore inappropriate to use this same
data to test the method. A cylinder of control gas of known composition, as described in 5.1.2.3, typical of the
natural gases for which the method is to be used, is required.
Carry out a control gas analysis with each batch of sample. Its composition is unvarying and so the results of this
analysis can be used as an indication as to whether the method is no longer working satisfactorily or recalibration is
necessary, or both. Before first use, analyse the control gas, using the method and WRM as specified, sufficient
times (at least 10) for precision data to be calculated. For each component in the control gas, calculate the mean
concentration and its standard deviation. These values should be typical of those that would be expected for this
control gas on subsequent occasions.
Assuming that the analytical results for the control gas follow a normal distribution, 68,3 % of any set of repeat
results should fall within + 1 standard deviation of the mean value, 95,4 % should fall within + 2 standard deviations
and 997 % should fall within + 3 standard deviations. In other words, while the system is behaving normally, an
individual result obtained on the control gas would fall outside + 3 standard deviations on only 3 occasions out
of 1 000. This is sufficiently rare for such a result to be
...

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