Natural gas - Determination of composition and associated uncertainty by gas chromatography - Part 5: Isothermal method for nitrogen, carbon dioxide, C1 to C5 hydrocarbons and C6+ hydrocarbons (ISO 6974-5:2014)

EN ISO 6974-5 describes a gas chromatographic method for the quantitative determination of the content of nitrogen, carbon dioxide and C1 to C5 hydrocarbons individually and a composite C6+ measurement, which represents all hydrocarbons of carbon number 6 and above in natural gas samples. It is applicable to the analysis of gases containing constituents within the working ranges given in Table 1.

Erdgas - Bestimmung der Zusammensetzung und der zugehörigen Unsicherheit durch Gaschromatographie - Teil 5: Isothermes Verfahren für Stickstoff, Kohlenstoffdioxid, C1- bis C5-Kohlenwasserstoffe und C6+-Kohlenwasserstoffe (ISO 6974-5:2014)

Dieser Teil dieser Internationalen Norm beschreibt ein gaschromatographisches Verfahren zur quantitativen Bestimmung des Gehalts an Stickstoff, Kohlenstoffdioxid und der individuellen C1- bis C5-Kohlenwasserstoffe und einer C6+-Verbundmessung, die alle Kohlenwasserstoffe mit sechs und mehr Kohlenwasserstoffatomen in Erdgasproben repräsentiert. Es ist anwendbar zur Analyse von Gasen, deren Bestandteile in den in Tabelle 1 angegebenen Arbeitsbereichen liegen.
Tabelle 1 - Messbereiche der Komponenten

Gaz naturel - Détermination de la composition et une incertitude définie par chromatographie en phase gazeuse - Partie 5: Méthode isotherme pour l'azote, le dioxyde de carbone, les hydrocarbures C1 à C5 et C6+ (ISO 6974-5:2014)

L'ISO 6974-5:2014 décrit une méthode chromatographique en phase gazeuse pour la détermination quantitative de la teneur en azote, du dioxyde de carbone et des hydrocarbures C1 à C5 individuellement, et une mesure composite des C6+ qui représente tous les hydrocarbures de 6 atomes de carbone et plus dans des échantillons de gaz naturel.

Zemeljski plin - Ugotavljanje sestave in pripadajoče negotovosti s plinsko kromatografijo - 5. del: Izotermična metoda za dušik, ogljikov dioksid, ogljikovodike C1 do C5 in ogljikovodike C6+ (ISO 6974-5:2014)

Standard EN ISO 6974-5 opisuje metodo s plinsko kromatografijo za kvantitativno ugotavljanje vsebnosti dušika, ogljikovega dioksida in posameznih ogljikovodikov C1 do C5 ter sestavljeno merjenje ogljikovodikov C6+, ki zajema vse ogljikovodike s številko 6 in več v vzorcih zemeljskega plina. Uporablja se za analizo plinov, ki vsebujejo sestavine v znotraj delovnih območij iz tabele 1.

General Information

Status
Published
Public Enquiry End Date
09-Oct-2012
Publication Date
10-Aug-2014
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
16-Jul-2014
Due Date
20-Sep-2014
Completion Date
11-Aug-2014

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SLOVENSKI STANDARD
SIST EN ISO 6974-5:2014
01-september-2014
1DGRPHãþD
SIST EN ISO 6974-5:2001
=HPHOMVNLSOLQ8JRWDYOMDQMHVHVWDYHLQSULSDGDMRþHQHJRWRYRVWLVSOLQVNR
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RJOMLNRYRGLNH&GR&LQRJOMLNRYRGLNH& ,62
Natural gas - Determination of composition and associated uncertainty by gas

chromatography - Part 5: Isothermal method for nitrogen, carbon dioxide, C1 to C5

hydrocarbons and C6+ hydrocarbons (ISO 6974-5:2014)
Erdgas - Bestimmung der Zusammensetzung und der zugehörigen Unsicherheit durch

Gaschromatographie - Teil 5: Isothermes Verfahren für Stickstoff, Kohlenstoffdioxid, C1-

bis C5-Kohlenwasserstoffe und C6+-Kohlenwasserstoffe (ISO 6974-5:2014)
*D]QDWXUHO'pWHUPLQDWLRQGHODFRPSRVLWLRQHWXQHLQFHUWLWXGHGpILQLHSDU
FKURPDWRJUDSKLHHQSKDVHJD]HXVH3DUWLH0pWKRGHLVRWKHUPHSRXUO
D]RWHOH
GLR[\GHGH
FDUERQHOHVK\GURFDUEXUHV&j&HW& ,62
Ta slovenski standard je istoveten z: EN ISO 6974-5:2014
ICS:
75.060 Zemeljski plin Natural gas
SIST EN ISO 6974-5:2014 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 6974-5:2014
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SIST EN ISO 6974-5:2014
EUROPEAN STANDARD
EN ISO 6974-5
NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2014
ICS 75.060 Supersedes EN ISO 6974-5:2001
English Version
Natural gas - Determination of composition and associated
uncertainty by gas chromatography - Part 5: Isothermal method
for nitrogen, carbon dioxide, C1 to C5 hydrocarbons and C6+
hydrocarbons (ISO 6974-5:2014)

Gaz naturel - Détermination de la composition et de Erdgas - Bestimmung der Zusammensetzung und der

l'incertitude associée par chromatographie en phase zugehörigen Unsicherheit durch Gaschromatographie - Teil

gazeuse - Partie 5: Méthode isotherme pour l'azote, le 5: Isothermes Verfahren für Stickstoff, Kohlenstoffdioxid,

dioxyde de carbone, les hydrocarbures C1 à C5 et C6+ C1- bis C5-Kohlenwasserstoffe und C6+-

(ISO 6974-5:2014) Kohlenwasserstoffe (ISO 6974-5:2014)
This European Standard was approved by CEN on 28 June 2014.

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 CEN-CENELEC Management Centre 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 CEN-CENELEC Management Centre has the same

status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United

Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2014 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6974-5:2014 E

worldwide for CEN national Members.
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SIST EN ISO 6974-5:2014
EN ISO 6974-5:2014 (E)
Contents Page

Foreword ..............................................................................................................................................................3

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SIST EN ISO 6974-5:2014
EN ISO 6974-5:2014 (E)
Foreword

This document (EN ISO 6974-5:2014) has been prepared by Technical Committee ISO/TC 193 "Natural gas".

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 January 2015, and conflicting national standards shall be withdrawn at

the latest by January 2015.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 6974-5:2001.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following

countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech

Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,

Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,

Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.

Endorsement notice

The text of ISO 6974-5:2014 has been approved by CEN as EN ISO 6974-5:2014 without any modification.

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SIST EN ISO 6974-5:2014
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SIST EN ISO 6974-5:2014
INTERNATIONAL ISO
STANDARD 6974-5
Second edition
2014-07-15
Natural gas — Determination
of composition and associated
uncertainty by gas chromatography —
Part 5:
Isothermal method for nitrogen,
carbon dioxide, C to C hydrocarbons
1 5
and C hydrocarbons
Gaz naturel — Détermination de la composition et de l’incertitude
associée par chromatographie en phase gazeuse —
Partie 5: Méthode isotherme pour l’azote, le dioxyde de carbone, les
hydrocarbures C à C et C
1 5 6+
Reference number
ISO 6974-5:2014(E)
ISO 2014
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2014

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form

or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior

written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of

the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2014 – All rights reserved
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 2

3 Principle ........................................................................................................................................................................................................................ 2

4 Materials ....................................................................................................................................................................................................................... 4

5 Apparatus ..................................................................................................................................................................................................................... 4

6 Scheme of the configuration ..................................................................................................................................................................... 6

7 Procedure..................................................................................................................................................................................................................... 7

7.1 Control of the apparatus ................................................................................................................................................................. 7

7.2 Operation of the apparatus .......................................................................................................................................................... 8

8 Expression of results .....................................................................................................................................................................................11

8.1 Uncertainty ..............................................................................................................................................................................................11

8.2 Test report ................................................................................................................................................................................................11

Annex A (informative) Example of application .......................................................................................................................................12

Annex B (informative) Procedure for Setting Valve timings and Restrictor Setting ........................................22

Bibliography .............................................................................................................................................................................................................................24

© ISO 2014 – All rights reserved iii
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(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 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 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 meaning of ISO specific terms and expressions related to conformity

assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers

to Trade (TBT), see the following URL: Foreword - Supplementary information

The committee responsible for this document is ISO/TC 193, Natural Gas, Subcommittee SC 1, Analysis

of Natural Gas.
This second edition cancels and replaces the first edition (ISO 6974-5:2000).

ISO 6974 consists of the following parts, under the general title Natural gas — Determination of

composition and associated uncertainty by gas chromatography:
— Part 1: General guidelines and calculation of composition
— Part 2: Uncertainty calculations

— Part 3: Determination of hydrogen, helium, oxygen, nitrogen, carbon dioxide and hydrocarbons up to C8

using two capillary columns and one packed column

— Part 4: Determination of nitrogen, carbon dioxide and C to C and C + hydrocarbons for a laboratory

1 5 6
and on-line measuring system using two columns

— Part 5: Isothermal method for nitrogen, carbon dioxide, C to C hydrocarbons and C + hydrocarbons

1 5 6

— Part 6: Determination of helium, oxygen, nitrogen, carbon dioxide and C to C hydrocarbons using three

1 8
capillary columns
iv © ISO 2014 – All rights reserved
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(E)
Introduction

This part of ISO 6974 describes a method for the analysis of natural gas that is commonly used for online

process applications, but can be applied to laboratory instruments. The compositional data obtained are

used for the calculation of calorific value, density and Wobbe index.

It is assumed that the natural gas does not contain any oxygen at source and that any oxygen which may

be present is due to contamination during sampling.

The primary use of this chromatographic method is the calculation of calorific value (CV) according

to ISO 6976. It is based on a column switching technique in which multiple columns, chosen for their

separating ability for particular groups of components, are switched under automatic control.

Only one injection is necessary and the first phase of the method involves accelerated backflush of C +

(which is measured as a recombined “pseudo component” rather than by the summation of individual

component measurements). Lighter components (nitrogen, methane, carbon dioxide and ethane) are

stored on the appropriate separating column while the heavier, C to C hydrocarbons are eluted. The

3 5

lighter components are then separated by redirecting carrier gas on to the appropriate column.

A Thermal Conductivity Detector (TCD) is used for measurement of the above components.

When the method is first set up, the repeatability of measurement is established by repetitive analysis of

a cylinder of test gas, commonly a typical natural gas. For each component, a control chart showing the

mean value, and the bounds representing 2 and 3 standard deviations, is drawn up. Subsequently, this

test gas is analysed after each calibration of the analyser, and the results are compared with the data in

the control charts. The performance of the analyser is assessed by this procedure.

Any change in the method setup can give rise to differences in component responses and hence (where

applied) to calculated uncertainties. In these circumstances fitting data to an existing control chart is

not a suitable procedure, and the operations that were undertaken when the method was first set up

shall be repeated.

This part of ISO 6974 provides one of the methods that may be used for determining the compositions of

natural gas in accordance with ISO 6974-1 and ISO 6974-2.
© ISO 2014 – All rights reserved v
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SIST EN ISO 6974-5:2014
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SIST EN ISO 6974-5:2014
INTERNATIONAL STANDARD ISO 6974-5:2014(E)
Natural gas — Determination of composition and
associated uncertainty by gas chromatography —
Part 5:
Isothermal method for nitrogen, carbon dioxide, C to C
1 5
hydrocarbons and C hydrocarbons
1 Scope

This part of this International Standard describes a gas chromatographic method for the quantitative

determination of the content of nitrogen, carbon dioxide and C to C hydrocarbons individually and

1 5

a composite C + measurement, which represents all hydrocarbons of carbon number 6 and above in

natural gas samples. It is applicable to the analysis of gases containing constituents within the working

ranges given in Table 1.
Table 1 — Component working ranges
Mole fraction
Component
Min. Max.
Nitrogen N 0,1 22
Carbon dioxide CO 0,05 15
Methane CH 34 100
Ethane C H 0,1 23
2 6
Propane C H 0,05 10
3 8
iso-Butane i-C H 0,01 2,0
4 10
n-Butane n-C H 0,01 2,0
4 10
neo-Pentane neo-C H 0,005 0,35
5 12
iso-Pentane i-C H 0,005 0,35
5 12
n-Pentane n-C H 0,005 0,35
5 12
Hexanes + C + 0,005 0,35

NOTE 1 The working ranges in Table 1 are those for which the method has been shown to

be satisfactory, and are offered for guidance. However, there is no reason why wider ranges

should not be used, provided that the successful measurement of such wider ranges has been

demonstrated.
NOTE 2 Hydrocarbons above n-pentane are expressed as the “pseudo-component” C +

which is measured as one composite peak and calibrated as such. The properties of C + are

calculated from an extended analysis of the individual C and higher hydrocarbons.

NOTE 3 Oxygen is not a normal constituent of natural gas and would not be expected to be

present in gas sampled to an online instrument. If any oxygen is present as a result of air

contamination, it will be measured with the nitrogen. The resulting measured (nitrogen +

oxygen) value will be in error to a small extent because of the slight difference between the

detector responses of oxygen and nitrogen.

NOTE 4 The helium and argon contents are assumed to be sufficiently small and unvarying

that they need not be analysed for.
NOTE 5 The gas sample shall not contain any hydrocarbon condensate and/or water.
© ISO 2014 – All rights reserved 1
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(E)
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

ISO 6974-1, Natural gas — Determination of composition and associated uncertainty by gas

chromatography — Part 1: General guidelines and calculation of composition

ISO 6974-2, Natural gas — Determination of composition and associated uncertainty by gas

chromatography — Part 2: Uncertainty calculations
3 Principle

Figure 1 is a flowchart showing the steps involved in the analytical process. It is based on more detailed

flowcharts in ISO 6974-1 and ISO 6974-2, simplified to represent the procedure described in this part.

References are given at each step to the relevant clause in this part and, where appropriate, to the

relevant clauses in ISO 6974-1 and ISO 6974-2.
2 © ISO 2014 – All rights reserved
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(E)
Figure 1 — Operational flowchart

NOTE The steps referred to in Figure 1 are identical to the steps in flowcharts A and B in ISO 6974-1 Step 5

refers to the use of relative response factors for indirectly measured components. Indirect components are not

used in this part of ISO 6974, so step 5 is not used.

The chromatographic method uses a column switching/backflush arrangement, configured as shown

in Figure 2. The sample is injected onto a boiling-point column which is divided into short and long

sections (columns 1 and 2). The long section (column 2) provides separation of C to C hydrocarbons,

3 5

while C and heavier hydrocarbons are retained on the short section (column 1), from which they are

© ISO 2014 – All rights reserved 3
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(E)

backflushed and measured by the detector as a single peak. Two six-port valves can handle the sample

injection and backflushing operations, or they may be dealt with together by a single 10-port valve.

Nitrogen, carbon dioxide, methane and ethane pass rapidly and unresolved through the boiling-point

column onto a porous polymer bead column (column 3), suitable for their separation. A six-port valve

either connects this column or by-passes it during measurement of C to C components.

3 5
The separations that occur in the columns are as follows:
Column 1 Retains C + components ready for backflushing as one composite peak.

Column 2 Separates Propane, iso-Butane, n-Butane, neo-Pentane, iso-Pentane and n-Pentane,

(which elute after C + has left column 1).

Column 3 Stores and separates Nitrogen, Methane, Carbon Dioxide and Ethane which elute after

n-Pentane has left column 2.
4 Materials
4.1 Carrier gas, Helium (He), ≥99,995 % pure, free from oxygen and water.

4.2 Auxiliary gases, compressed air, for valve actuation (If consumption is low, carrier gas may be used

as an alternative for valve actuation).
4.3 Reference materials.
4.3.1 Reference gases, according to ISO 6974-1.

4.3.2 Gas mixture containing n-Pentane and 2,2-Di-Me-butane, used to check valve timings (see

Annex B).
5 Apparatus
5.1 Gas chromatograph, capable of isothermal operation and equipped with TCD.

5.2 Column oven, temperature range 70 °C to 105 °C, capable of being maintained to within ±0,1 °C.

5.3 Valve oven, controlled over the temperature range 70 °C to 105 °C, or valves fitted in the column

oven.
5.4 Pressure regulator, to give suitable carrier gas flow rates
5.5 Injection device, V1, six-port sample injection valve

5.6 Backflush valve, V2, six-port, to allow rapid backflush of C + components. As described in section

3, a single 10-port valve may be used for both these tasks. The operating principle is the same.

5.7 Column isolation valve, V3, six-port. This directs the carrier gas through the porous polymer bead

column (column 3), or by-passes it.

5.8 Columns, The columns must satisfy the performance requirements given in 7.2.4. The following

packing materials and column dimensions, given as examples, should be satisfactory, for use with

conventional and readily available injection valves and TCDs. Any alternative combination of columns

which provide similar separations and satisfy the performance requirements may be used. Micro-packed

4 © ISO 2014 – All rights reserved
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(E)

or even capillary columns can be chosen, with appropriately sized injection and detector systems, in

which case packing or coating details would be different.
5.9 Tube and packing.
5.9.1 Configuration 1

5.9.1.1 Column 1, 28 % DC200/500 on 45/60 mesh chromosorb P-AW, 0,75 m (2,5 foot) long, 2 mm i.d.

(1/8 in o.d.).

5.9.1.2 Column 2, 28 % DC200/500 on 45/60 mesh chromosorb P-AW, 5,2 m (17 foot) long, 2 mm i.d.

(1/8 in o.d.).

5.9.1.3 Column 3, 15 % DC200/500 on 50/80 mesh Porapak N, 2,4 m (8 ft) long, 2 mm i.d. (1/8 in o.d.).

5.9.2 Configuration 2.

5.9.2.1 Column 1, oxy-diproprionitrile on Porasil C, 0,3 m (1 foot) long, 0,75 mm i.d. (1/16 in o.d.).

5.9.2.2 Column 2, 20 % SF-96 on 80-100 mesh chromosorb W, 2,1 m (7 foot) long, 0,75 mm i.d. (1/16

in o.d.).
5.9.2.3 Column 3, HayeSep N, 2,1 m (7 foot) long, 0,75 mm i.d. (1/16 in o.d.).

5.10 Method of packing, any method which results in uniform column packing may be used.

NOTE The following method is suitable.

The column outlet is closed with a sintered disc or glass wool plug. A reservoir containing rather more

packing than is needed to fill the column is connected to the inlet and a pressure of 0,4 MPa of nitrogen is

applied to this reservoir. The flow of packing into the column is assisted by vibration. When the column

is full, allow the pressure to decay slowly before disconnecting the reservoir.

5.11 Thermal Conductivity Detector (TCD), with a time constant of not greater than 0,1 s, and internal

volume appropriate for the column sizes and flow rate used.

5.12 Controller/Peak Measurement System. Wide range (0 V to 1 V), capable of measuring peaks on a

sloping baseline. Be enabled to control automatic operation of the valves according to a sequence selected

by the operator.

5.13 Auxiliary valves, tubing and other accessories, to control the flow of sample gas to the

chromatograph and for shutting off this flow for a defined period of time before injection.

© ISO 2014 – All rights reserved 5
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(E)
6 Scheme of the configuration
a) Initial configuration: all valves in position 1
b) Sample injection: V1 to position 2
c) Backflush C +: V2 to position 2
6 © ISO 2014 – All rights reserved
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(E)
d) Isolate N , C , CO , C ; measure C to C : V3 to position 2
2 1 2 2 3 5
e) Reconnect column 3 - measure N , C , CO , C :V3 to position 1
2 1 2 2
Figure 2 — Scheme of the configuration
7 Procedure
7.1 Control of the apparatus
Set up the gas chromatograph according to the manufacturer’s instructions.
7.1.1 Column Conditioning

The columns described in 5.8 and 5.9 do not need conditioning or activation, and are generally being

used well within their temperature limits. However a small amount of column bleed due to lower-

boiling impurities may be evident on first use, and result in unstable baselines. Operation of the analyser

overnight with carrier gas flowing but no sample injections, at a temperature 20 °C to 40 °C above the

recommended operating temperature should eliminate this effect.

Residual adsorbed moisture in the lines supplying carrier gas or sample gas can give rise to unexplained

peaks over and above those expected. Operation overnight under the recommended conditions with

sample injection should eliminate these effects.
© ISO 2014 – All rights reserved 7
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(E)
7.2 Operation of the apparatus
7.2.1 Analytical method

Examples of the operating conditions for configurations 1 (5.9.1) and 2 (5.9.2) are given in Tables 2 and

Table 2 — Example of instrument conditions, configuration 1
Column 1 Column 2 Column 3

Stationary phase Silicone oil DC 200/500 Silicone oil DC 200/500 Silicone oil DC 200/500

Loading % 28 % 28 % 15 %
Support Chromosorb P-AW Chromosorb P-AW
Active solid Porapak N
ASTM mesh size 45/60 45/60 50/80
Column length 0,75 m 5,2 m 2,4 m
Column i.d. 2 mm 2 mm 2 mm
material Stainless steel
Temperature 100 °C
Carrier gas Helium
Supply pressure 4 bar
Flowrate 28 ml/min
Detector Thermal Conductivity
Detector Temp. 100 °C minimum
Injection device Valve
Injector Temp. 100 °C
Sample size 1,0 ml
8 © ISO 2014 – All rights reserved
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SIST EN ISO 6974-5:2014
ISO 6974-5:2014(E)
Table 3 — Example of instrument conditions, configuration 2
Column 1 Column 2 Column 3
Stationary phase Oxy-diproprionitrile Silicone oil SF-96 Silicone oil DC 200/500
Loading % 28 % 20 % 15 %
Support Chromosorb P-AW
Active solid Porasil C HayeSep N
ASTM mesh size 80/100 80/100 80/100
Column length 0,3 m 2,1 m 2,1 m
Column i.d. 0,75 mm 0,75 mm 0,75 mm
material Stainless steel
Temperature 80 °C
Carrier gas Helium
Supply pressure 4 bar
Flowrate 28 ml/min
Detector Thermal Conductivity
Detector Temp. 80 °C minimum
Injection device Valve
Injector Temp. 80 °C
Sample size 0,25 ml
7.2.2 Sample introduction

Purge the sample valve with the gas to be analysed, using at least 20 times the volume of the valve and

associated pipe work.

Stop the purge to enable the gas to reach the temperature of the valve and ambient pressure, and then

start the analytical cycle, injecting the sample and switching the valves as required.

If this volume of sample is not enough to purge the valve, then contamination by air or by the previous

sample will be evident. If either occurs, then use a larger volume of sample for purging.

NOTE The sample loop should be purged with gas for a precise time, at a defined rate, and the sample should

then be allowed to equilibrate to ambient pressure before injection. In the absence of equipment which can

confirm the latter, there should be a defined time between sample valve shut off and injection.

7.2.3 Analysis

The analytical system shown in Figure 2 consists of one six-port sample injection valve, V1, one six-port

backflush valve, V2, and one six-port by-pass valve V3. Restrictor A maintains the pneumatic balance of

the system when column 3 is isolated. The detailed setting-up procedure is given in Annex B. (One 10-

port valve may be used in place of the six-port valves V1 and V2, controlling both sample injection and

backflushing of column 1.).
The timings of the valve switching operations must ensure that:

a) V2 is returned to the backflush position (position 2) after all the n-pentane leaves column 1 but

before the lowest C isomer leaves column 1 on its way to column 2.

b) V3 is switched to isolate column 3 (position 2) before any propane leaves column 2 (on its way to

column 3) and after all the ethane has left column 2 and entered column 3.
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