SIST EN ISO 6974-1:2012

Natural gas - Determination of composition and associated uncertainty by gas chromatography - Part 1: General guidelines and calculation of composition (ISO 6974-1:2012)

This part of ISO 6974 gives methods for calculating component mole fractions of natural gas and specifies the data processing requirements for determining component mole fractions. This part of ISO 6974 provides for both single and multiple operation methods and either multi-point calibration or a performance evaluation of
the analyser followed by single-point calibration. This part of ISO 6974 gives procedures for the calculation of the raw and processed (e.g. normalized) mole fractions, and their associated uncertainties, for all components. The procedures given in this part of ISO 6974 are applicable to the handling of data obtained from replicate or
single analyses of a natural gas sample.

Erdgas - Bestimmung der Zusammensetzung und der zugehörigen Unsicherheit durch Gaschromatographie - Teil 1: Allgemeine Leitlinien und Berechnung der Zusammensetzung (ISO 6974-1:2012)

Dieser Teil von ISO 6974 gibt Verfahren für die Berechnung von Komponenten-Molfraktionen von Erdgas vor und legt Anforderungen an die Datenverarbeitung zur Bestimmung der Komponenten-Molfraktionen fest. Dieser Teil von ISO 6974 deckt sowohl Einfach- und Mehrfachbestimmung als auch und entweder Mehrpunktkalibrierung oder eine Leistungsbewertung des Analysegerätes, gefolgt von einer Einpunktkalibrierung, ab. Dieser Teil von ISO 6874 enthält Verfahrensweisen für die Berechnung der unbearbeiteten und der bearbeiteten (z. B. normalisierten) Molfraktionen sowie der zugehörigen Unsicherheiten für alle Komponenten. Die in diesem Teil von ISO 6974 enthaltenen Verfahrensweisen sind anwendbar, um Daten aus Wiederhol  oder Einzelanalysen von Erdgasproben zu bearbeiten.

Gaz naturel - Détermination de la composition avec une incertitude définie par chromatographie en phase gazeuse - Partie 1: Lignes directrices générales et calculs de la composition (ISO 6974-1:2012)

L'ISO 6974-1:2012 donne des méthodes de calcul des fractions molaires des constituants du gaz naturel et spécifie les exigences de traitement des données pour déterminer les fractions molaires des constituants.
L'ISO 6974-1:2012 fournit à la fois des méthodes d'analyse unique et multiple, mais aussi un étalonnage multipoint, ou une évaluation des performances de l'analyseur suivie d'un étalonnage en un seul point.
L'ISO 6974‑1:2012 indique les procédures pour le calcul des fractions molaires brutes et traitées (par exemple normalisées), et des incertitudes associées, pour tous les constituants. Les procédures données dans l'ISO 6974‑1:2012 s'appliquent au traitement des données obtenues à partir d'analyses uniques ou répétées d'un échantillon de gaz naturel.

Zemeljski plin - Določevanje sestave in pripadajoče negotovosti s plinsko kromatografijo - 1. del: Splošne smernice in računanje sestave (ISO 6974-1:2012)

Ta del standarda ISO 6974 določa metode za računanje molskih frakcij sestavin zemeljskega plina in določa zahteve za obdelavo podatkov za določevanje molskih frakcij sestavin. Ta del standarda ISO 6974 določa posamezne in večkratne operacijske metode ter bodisi večtočkovno umerjanje bodisi delovno oceno analizatorja, ki ji sledi enotočkovno umerjanje. Ta del standarda ISO 6974 določa postopke za računanje surovih in predelanih (tj. normaliziranih) molskih frakcij in njihovih povezanih negotovosti za vse sestavine. Postopki iz tega dela standarda ISO 6974 se uporabljajo za obdelavo podatkov iz ponovljenih ali posameznih analiz vzorca zemeljskega plina.

General Information

• Status: Published
• Public Enquiry End Date: 14-Jul-2010
• Publication Date: 12-Jun-2012
• ICS: 75.060 - Natural gas
• Technical Committee: NAD - Petroleum products, lubricants and related products
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 28-May-2012
• Due Date: 02-Aug-2012
• Completion Date: 13-Jun-2012
• Ref Project: EN ISO 6974-1:2012 - Natural gas - Determination of composition and associated uncertainty by gas chromatography - Part 1: General guidelines and calculation of composition (ISO 6974-1:2012)

Relations

• Replaces: SIST EN ISO 6974-1:2001 - Natural gas - Determination of composition with defined uncertainty by gas chromatography - Part 1: Guidelines for tailored analysis (ISO 6974-1:2000)
• Effective Date: 01-Jul-2012
• Corrected By: SIST EN ISO 6974-1:2012/AC:2013 - Natural gas - Determination of composition and associated uncertainty by gas chromatography - Part 1: General guidelines and calculation of composition - Technical Corrigendum 1 (ISO 6974-1:2012/Cor 1:2012)
• Effective Date: 01-Feb-2013

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 6974-1:2012
01-julij-2012
1DGRPHãþD
SIST EN ISO 6974-1:2001
=HPHOMVNLSOLQ'RORþHYDQMHVHVWDYHLQSULSDGDMRþHQHJRWRYRVWLVSOLQVNR
NURPDWRJUDILMRGHO6SORãQHVPHUQLFHLQUDþXQDQMHVHVWDYH,62
Natural gas - Determination of composition and associated uncertainty by gas
chromatography - Part 1: General guidelines and calculation of composition (ISO 6974-
1:2012)
Erdgas - Bestimmung der Zusammensetzung und der zugehörigen Unsicherheit durch
Gaschromatographie - Teil 1: Allgemeine Leitlinien und Berechnung der
Zusammensetzung (ISO 6974-1:2012)
Gaz naturel - Détermination de la composition avec une incertitude définie par
chromatographie en phase gazeuse - Partie 1: Lignes directrices générales et calculs de
la composition (ISO 6974-1:2012)
Ta slovenski standard je istoveten z: EN ISO 6974-1:2012
ICS:
75.060 Zemeljski plin Natural gas
SIST EN ISO 6974-1:2012 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 6974-1:2012

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SIST EN ISO 6974-1:2012


EUROPEAN STANDARD
EN ISO 6974-1

NORME EUROPÉENNE

EUROPÄISCHE NORM
May 2012
ICS 75.060 Supersedes EN ISO 6974-1:2001
English Version
Natural gas - Determination of composition and associated
uncertainty by gas chromatography - Part 1: General guidelines
and calculation of composition (ISO 6974-1:2012)
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 1: Lignes directrices générales et calcul 1: Allgemeine Leitlinien und Berechnung der
de la composition (ISO 6974-1:2012) Zusammensetzung (ISO 6974-1:2012)
This European Standard was approved by CEN on 14 May 2012.

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, 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

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2012 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6974-1:2012: E
worldwide for CEN national Members.

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SIST EN ISO 6974-1:2012
EN ISO 6974-1:2012 (E)
Contents Page
Foreword .3

2

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SIST EN ISO 6974-1:2012
EN ISO 6974-1:2012 (E)
Foreword
This document (EN ISO 6974-1:2012) 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 November 2012, and conflicting national standards shall be withdrawn
at the latest by November 2012.
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 6974-1:2001.
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, 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 6974-1:2012 has been approved by CEN as a EN ISO 6974-1:2012 without any modification.


3

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SIST EN ISO 6974-1:2012

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SIST EN ISO 6974-1:2012
INTERNATIONAL ISO
STANDARD 6974-1
Second edition
2012-05-15
Natural gas — Determination of
composition and associated uncertainty
by gas chromatography —
Part 1:
General guidelines and calculation of
composition
Gaz naturel — Détermination de la composition et de l’incertitude
associée par chromatographie en phase gazeuse —
Partie 1: Lignes directrices générales et calcul de la composition
Reference number
ISO 6974-1:2012(E)
©
ISO 2012

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SIST EN ISO 6974-1:2012
ISO 6974-1:2012(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2012
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 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 [e-mail]
Web www.iso.org
Published in Switzerland
ii © ISO 2012 – All rights reserved

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SIST EN ISO 6974-1:2012
ISO 6974-1:2012(E)
Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 5
4.1 Symbols . 5
4.2 Subscripts . 6
5 Principles of analysis . 6
5.1 General considerations . 6
5.2 Method of operation. 7
5.3 Mode of operation . 8
5.4 Directly and indirectly measured components . 8
5.5 Normalization . 8
6 Analytical procedure . 8
6.1 General considerations . 8
6.2 Step 1 — Defining the working range .10
6.3 Step 2 — Defining the requirements of the analytical method . 11
6.4 Step 3 — Selecting equipment and working conditions . 11
6.5 Step 4 — Response characteristics (primary calibration or performance evaluation) .12
6.6 Step 5 — Relative response factors .15
6.7 Step 6 — Routine calibration/quality assurance check .16
6.8 Step 7 — Analysis of samples .17
6.9 Step 8 — Calculation of component mole fractions .18
7 Control chart .21
8 Test report .21
Annex A (informative) Comparative application ranges and characteristics of analytical methods
described in ISO 6974-3 to ISO 6974-6 .23
Annex B (informative) Alternative approach to bridging and normalization .25
Annex C (informative) Methane-by-difference approach .32
Annex D (normative) Relative response factors .33
Annex E (informative) Testing for outliers .35
Annex F (normative) Pressure correction during calibration and sample analysis .36
Annex G (informative) Software suitable for generalized least squares regression analysis .38
Annex H (informative) Use of control charts .40
Bibliography .41
© ISO 2012 – All rights reserved iii

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SIST EN ISO 6974-1:2012
ISO 6974-1:2012(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. 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.
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.
ISO 6974-1 was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 1, Analysis
of natural gas.
This second edition of ISO 6974-1, together with ISO 6974-2:2012, cancels and replaces ISO 6974-1:2000 and
ISO 6974-2:2001, which have been technically revised.
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 C
8
using two packed columns
— Part 4: Determination of nitrogen, carbon dioxide and C to C and C hydrocarbons for a laboratory and
1 5 6+
on-line measuring system using two columns
— Part 5: Determination of nitrogen, carbon dioxide and C to C and C hydrocarbons for a laboratory and
1 5 6+
on-line process application using three columns
— Part 6: Determination of hydrogen, helium, oxygen, nitrogen, carbon dioxide and C to C hydrocarbons
1 8
using three capillary columns
Future subsequent parts of ISO 6974 are planned.
iv © ISO 2012 – All rights reserved

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SIST EN ISO 6974-1:2012
ISO 6974-1:2012(E)
Introduction
ISO 6974 describes methods of analysis of natural gas and methods for calculating component mole fractions
and uncertainties. ISO 6974 is intended for the measurement of H , He, O , N , CO and hydrocarbons, either as
2 2 2 2
individual components or as a group, for example all hydrocarbons above C , defined as C . This approach is
5 6+
suitable for a range of end applications, including calibrating gas mixtures and providing natural gas composition
and uncertainty data to be used in the calculation of calorific value and other additive physical properties of the
gas. Details of these end applications are provided in ISO 6974-3 and subsequent parts of ISO 6974.
This part of ISO 6974 gives guidelines for the gas chromatographic analysis of natural gas and methods of data
processing to determine compositions of component mole fractions.
ISO 6974-2 describes the steps required to calculate the uncertainty of each component mole fraction.
ISO 6974-3 and subsequent parts of ISO 6974 describe different gas chromatographic methods. These
methods cover both daily practice in the laboratory and on-line field applications. In this part of ISO 6974,
Annex A provides a comparison of the characteristics of the analytical methods described in ISO 6974-3 and
subsequent parts of ISO 6974.
In cases where only component mole fractions are required, it is intended that this part of ISO 6974 be used in
conjunction with a gas chromatographic method of analysis, e.g. ISO 6974-3 or subsequent parts of ISO 6974.
In cases where component mole fractions and associated uncertainties are required, it is intended that this part
of ISO 6974 be used in conjunction with ISO 6974-2, in addition to a gas chromatographic method of analysis.
This part of ISO 6974 describes all the essential steps for setting up an analysis, including outlining the structure
of the analysis, defining the working ranges and establishing the analytical procedure. When the working
ranges of the components have been defined, an evaluation is carried out to determine whether components
are to be considered as
— main components or groups of components to be analysed using direct measurement (directly
measured components),
— components or groups of components to be analysed using indirect measurement, by reference to a
different reference component in the calibration gas mixture (indirectly measured components), or
— components that are not measured and whose mole fraction can be assumed to be constant (components
not measured).
This part of ISO 6974 provides for the use of three types of method: single operation, multiple operation
with bridging and multiple operation without bridging. The last of these methods is a special case of a single
operation method.
This part of ISO 6974 describes the conventional normalization approach for calculating processed mole
fractions from raw mole fractions (see 5.5). When conventional normalization is used for multiple operations
without bridging methods, the uncertainties of the calculated mole fractions will be conservative. If a more
accurate assessment of uncertainty is required, an alternative approach for normalization, using the generalized
least squares (GLS) method, can be used; this is described in Annex B, which is intended to be used when
calculating uncertainties in accordance with ISO 6974-2. Further alternative approaches are available for
calculating processed mole fractions, including methane-by-difference (see Annex C) and data harmonization
(see Reference [1]).
© ISO 2012 – All rights reserved v

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SIST EN ISO 6974-1:2012

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SIST EN ISO 6974-1:2012
INTERNATIONAL STANDARD ISO 6974-1:2012(E)
Natural gas — Determination of composition and associated
uncertainty by gas chromatography —
Part 1:
General guidelines and calculation of composition
1 Scope
This part of ISO 6974 gives methods for calculating component mole fractions of natural gas and specifies the
data processing requirements for determining component mole fractions. This part of ISO 6974 provides for
both single and multiple operation methods and either multi-point calibration or a performance evaluation of
the analyser followed by single-point calibration. This part of ISO 6974 gives procedures for the calculation of
the raw and processed (e.g. normalized) mole fractions, and their associated uncertainties, for all components.
The procedures given in this part of ISO 6974 are applicable to the handling of data obtained from replicate or
single analyses of a natural gas sample.
2 Normative references
The following referenced documents are indispensable for the application 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/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
ISO 6143, Gas analysis — Comparison methods for determining and checking the composition of
calibration gas mixtures
ISO 10723, Natural gas — Performance evaluation for on-line analytical systems
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
response
y
output signal of the measuring system for a component that is measured as peak area or peak height
3.2
reference component
component present in a certified reference gas mixture (CRM) (see 3.10), which is used to calibrate the analyser
response to other similar components in the sample which are not themselves present in the CRM
NOTE For example, if the CRM contains hydrocarbons up to and including n-butane, but no pentanes or higher, then
n-butane contained in the CRM can be used as a reference component for the quantification of pentanes and heavier
components in the sample. The reference component should have a response function that normally is a first-order
polynomial with zero intercept, i.e. a straight line through the origin.
© ISO 2012 – All rights reserved 1

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SIST EN ISO 6974-1:2012
ISO 6974-1:2012(E)
3.3
relative response factor
K
ratio of the molar amount of component j to the molar amount of reference component which gives an equal
detector response
NOTE 1 Relative response factors for flame ionization detectors are calculated as the ratio between the carbon number
of the reference component and the carbon number of the sample component (see D.1).
NOTE 2 Relative response factors for thermal conductivity detectors are determined experimentally (see D.2).
3.4
other components
components in the gas sample which are not measured by analysis in accordance with ISO 6974 and/or can
be regarded as being present at a constant mole fraction
3.5
group of components
components with mole fractions so low that their measurement as individuals would be difficult or require
excessive time, and which are therefore measured as a group
NOTE This can be achieved by particular chromatographic techniques, such as backflushing, or by data handling,
such as integrating a succession of components as if they were a single component.
3.6
uncertainty (of measurement)
parameter, associated with the result of a measurement, that characterizes the dispersion of the values that
could reasonably be attributed to the measurand
NOTE 1 The parameter may be, for example, a standard deviation (or a given multiple of it), or the half-width of an
interval having a stated level of confidence.
NOTE 2 Uncertainty of measurement comprises, in general, many components. Some of these components may be
evaluated from the statistical distribution of the results of series of measurements and can be characterized by experimental
standard deviations. The other components, which also can be characterized by standard deviations, are evaluated from
assumed probability distributions based on experience or other information.
NOTE 3 It is understood that the result of the measurement is the best estimate of the value of the measurand, and that
all components of uncertainty, including those arising from the systematic effects, such as components associated with
corrections and reference standards, contribute to the dispersion.
[ISO/IEC Guide 98-3:2008, 2.2.3]
3.7
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
[ISO/IEC Guide 98-3:2008, 2.3.1]
3.8
combined standard uncertainty
standard uncertainty of the result of a measurement when that result is obtained from the values of a number
of other quantities, equal to the positive square root of a sum of terms, the terms being the variances or
covariances of these other quantities weighted according to how the measurement result varies with changes
in these quantities
[ISO/IEC Guide 98-3:2008, 2.3.4]
2 © ISO 2012 – All rights reserved

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SIST EN ISO 6974-1:2012
ISO 6974-1:2012(E)
3.9
expanded uncertainty
quantity defining an interval about the result of a measurement that may be expected to encompass a large
fraction of the distribution of values that could reasonably be attributed to the measurand
NOTE 1 The fraction may be viewed as the coverage probability or level of confidence of the interval.
NOTE 2 To associate a specific level of confidence with the interval defined by the expanded uncertainty requires
explicit or implicit assumptions regarding the probability distribution characterized by the measurement result and its
combined standard uncertainty. The level of confidence that may be attributed to this interval can be known only to the
extent to which such assumptions may be justified.
[2]
NOTE 3 Expanded uncertainty is termed overall uncertainty in Recommendation INC-1 (1980) , Paragraph 5.
[ISO/IEC Guide 98-3:2008, 2.3.5]
3.10
certified reference gas mixture
CRM
reference gas mixture, characterized by a metrologically valid procedure for one or more specified properties,
accompanied by a certificate that provides the value of the specified property, its associated uncertainty, and
a statement of metrological traceability
[3]
NOTE 1 The above definition is based on the definition of “certified reference material” in ISO Guide 35 . “Certified
reference material” is a generic term; “certified reference gas mixture” is more suited to this application.
NOTE 2 The concept of value includes qualitative attributes such as identity or sequence. Uncertainties for such
attributes may be expressed as probabilities.
NOTE 3 Metrologically valid procedures for the production and certification of reference materials (such as certified
[4] [3]
reference gas mixtures) are given in, among others, ISO Guide 34 and ISO Guide 35 .
[5]
NOTE 4 ISO Guide 31 gives guidance on the contents of certificates.
3.11
working measurement standard
WMS
measurement standard that is used routinely to calibrate or verify measuring instruments or measuring systems
[6]
[ISO/IEC Guide 99:2007 , 5.7]
NOTE In ISO 6974, a working measurement standard is a CRM that is used to perform a routine calibration or a
quality assurance check (see 6.7).
3.12
direct measurement
measurement by which individual components and/or groups of components are determined by comparison
with identical components in the CRM(s)
3.13
indirect measurement
measurement by which individual components and/or groups of components which are themselves not present
in the CRM(s) are determined using relative response factors to a reference component in the CRM(s)
3.14
repeatability (of results of measurements)
closeness of the agreement between the results of successive measurements of the same measurand carried
out under the same conditions of measurement
NOTE 1 These conditions are called repeatability conditions.
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SIST EN ISO 6974-1:2012
ISO 6974-1:2012(E)
NOTE 2 Repeatability conditions include:
— the same measurement procedure
— the same observer
— the same measuring instrument, used under the same conditions
— the same location
— repetition over a short period of time.
NOTE 3 Repeatability may be expressed quantitatively in terms of the dispersion characteristics of the results.
[ISO/IEC Guide 98-3:2008, B.2.15]
3.15
working range
restricted mole fraction range specified for the methods described in ISO 6974
3.16
raw mole fraction
*
x
mole fraction of each component before the application of a process to correct the sum of the mole fractions to unity
NOTE The process of correcting the sum of mole fractions to unity is normalization or, less commonly, methane
by difference.
3.17
processed mole fraction
mole fraction of each component after the application of a process to correct the sum of the mole fractions to unity
NOTE The process of correcting the sum of mole fractions to unity is normalization or, less commonly, methane
by difference.
3.18
bridge component
component selected to allow the combination (“bridging”) of results for components measured by different
analytical operations
NOTE The different operations may be two or more sample injections and/or two or more detectors.
3.19
conventional normalization
normalization whereby the sum of raw mole fractions are corrected to unity by applying the same proportional
adjustment to all measured components.
NOTE A full description of conventional normalization is given in 5.5.
3.20
mean normalization
method of normalization whereby the repeat analyses for each component are averaged to form a series mean
and these mean values are then normalized
NOTE Treatment of data using this method is described in 6.9.2.
3.21
run-by-run normalization
method of normalization whereby each repeat analysis is normalized independently and the average of these
normalized values is then calculated
NOTE Treatment of data using this method is described in 6.9.3.
4 © ISO 2012 – All rights reserved

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SIST EN ISO 6974-1:2012
ISO 6974-1:2012(E)
4 Symbols
4.1 Symbols
a
coefficients of the regression function (z = 0, 1, 2 or 3)
z
A
intermediate matrix constructed from Σ and B (see Annex B)
b
parameters of the regression function (z = 0, 1, 2 or 3)
z
b′
parameters of the regression function corrected after routine calibration (Type 1 analyses)
z
mean parameters of the regression function (in “mean normalization” method)
b
z
B
matrix containing constraints (see Annex B)
D
intermediate matrix (see Annex B)
H
intermediate matrix constructed from Y, D and Σ (see Annex B)
k coverage factor
K relative response factor with respect to the reference component
n total number of bridge components
bc
n
bc
 
total number of duplicate measurements of all bridge components ( n −1 )
∑ du()bc
n  i 
du,bc
i=1
(see Annex B)
n total number of duplicate measurements (of the bridge component in parentheses)
du(…)
(see Annex B)
n total number of components (direct plus indirect, but excluding “other components”)
i
n total number of injections (and therefore total number of responses)
l
p pressure
P parameter (see Annex H)
s standard deviation
T sum of raw mole fractions of all componen
...