SIST EN ISO 10723:2002
(Main)Natural gas - Performance evaluation for on-line analytical systems (ISO 10723:1995, including Technical Corrigendum 1:1998)
Natural gas - Performance evaluation for on-line analytical systems (ISO 10723:1995, including Technical Corrigendum 1:1998)
Describes a method of assessing whether an analytical system for natural gas is satisfactory provided that the analytical requirements have been clearly defined and the analytical and calibration procedures have been fully described.
Erdgas - Bewertung der Leistungsfähigkeit von On-line-Analysensystemen (ISO 10723:1995, einschließlich Technische Korrektur 1:1998)
Diese Internationale Norm legt ein Verfahren fest, mit dessen Hilfe ermittelt werden kann, ob ein Erdgas-Analysesystem zufriedenstellend arbeitet, und zwar unter den Voraussetzungen, dass
a) die analytischen Anforderungen in Bezug auf den Bereich und die Unsicherheit der Messung der Konzentration der Komponenten sowie der Unsicherheit der aus diesen Messungen berechneten Eigenschaftsgrößen klar und eindeutig definiert sind;
b) das Analyse- sowie das Kalibrierverfahren vollständig beschrieben sind;
c) die Methode dazu bestimmt ist, auf Gase angewendet zu werden, deren Zusammensetzung in Bereichen variiert, wie man sie im Normalfall in Transport- und Versorgungsnetzen vorfindet.
Sofern das Verfahren zur Leistungsbewertung das System als nicht zufriedenstellend einschätzt, sind alle Etappen, nämlich
die analytischen Anforderungen,
das Analyseverfahren,
die Geräteauswahl,
die Auswahl der Kalibriergase,
das Berechnungsverfahren,
unter dem Blickwinkel der Testergebnisse zu überprüfen, um zu beurteilen, wo Verbesserungen erreicht werden können.
Diese Internationale Norm ist auf Analysesysteme anwendbar, die die Konzentrationen der Komponenten sowie deren Unsicherheiten liefern. Nach jetzigem Stand des Wissens wird das Verfahren der Wahl wohl am ehesten die Gaschromatographie sein.
Die Bewertung der Leistungsfähigkeit eines Analysesystems sollte während des Systemaufbaus, danach in Abhängigkeit vom Anwendungsbereich in regelmäßigen Abständen und/oder immer dann erfolgen, wenn ein kritischer Bestandteil des Analysesystems verändert oder ausgetauscht worden ist.
Gaz naturel - Evaluation des performances des systemes d'analyse en ligne (ISO 10723:1995, Rectificatif Technique 1:1998 inclus)
Zemeljski plin – Vrednotenje zmogljivosti “on-line” analitskih sistemov (ISO 10723:1995)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 10723:2002
01-december-2002
Zemeljski plin – Vrednotenje zmogljivosti “on-line” analitskih sistemov (ISO
10723:1995)
Natural gas - Performance evaluation for on-line analytical systems (ISO 10723:1995,
including Technical Corrigendum 1:1998)
Erdgas - Bewertung der Leistungsfähigkeit von On-line-Analysensystemen (ISO
10723:1995, einschließlich Technische Korrektur 1:1998)
Gaz naturel - Evaluation des performances des systemes d'analyse en ligne (ISO
10723:1995, Rectificatif Technique 1:1998 inclus)
Ta slovenski standard je istoveten z: EN ISO 10723:2002
ICS:
75.060 Zemeljski plin Natural gas
SIST EN ISO 10723:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 10723:2002
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SIST EN ISO 10723:2002
EUROPEAN STANDARD
EN ISO 10723
NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2002
ICS 75.060
English version
Natural gas - Performance evaluation for on-line analytical
systems (ISO 10723:1995)
Gaz naturel - Evaluation des performances des systèmes Erdgas - Bewertung der Leistungsfähigkeit von On-line-
d'analyse en ligne (ISO 10723:1995) Analysensystemen (ISO 10723:1995)
This European Standard was approved by CEN on 19 August 2002.
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 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 Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, 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
© 2002 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 10723:2002 E
worldwide for CEN national Members.
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SIST EN ISO 10723:2002
EN ISO 10723:2002 (E)
CORRECTED 2002-11-13
Foreword
The text of ISO 10723:1995 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 10723:2002 by the Technical Board of CEN.
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 March 2003, and conflicting national
standards shall be withdrawn at the latest by March 2003.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium, Czech
Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg,
Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 10723:1995 has been approved by CEN as EN ISO 10723:2002 without any
modifications.
2
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SIST EN ISO 10723:2002
INTERNATIONAL
ISO
STANDARD
10723
First edition
1995-12-15
Natura1 gas - Performance evaluation for
on-line analytical Systems
Gaz na turel - haluation des petformances des systemes d ’analyse en
ligne
Reference number
ISO 10723: 1995(E)
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SIST EN ISO 10723:2002
ISO 10723:1995(E)
Contents
Page
1 Scope .
....................... .................. 1
2 Normative references . .
......................... .......... 1
..........................................
3 Principle . . . 2
4 Suitability of analytical Systems
....... ......................................... 2
. . . . . . . . . . . . . . . . . . .*.m.
5 Test gases .I. 3
. . . . . . . . . . . . . . . .
5.1 Definition
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2 Test gas compositions . . . . . . . . . . . . . . . . . . . . . . .*. 4
6 Test procedures . . . . . . . . . . .
5
6.1 System efficiency test . .
5
6.2 Repeatability . . . . . . . . . . . . . .
6
6.3 Response concentration relationship .
9
6.4 Component separationlinterference
..................................... 13
7 Evaluation of results . . .
14
7.1 System efficiency .
................................. 14
7.2 Repeatability . .
................. 14
7.3 Response/concentration relationship
................................... 14
7.4 Component separation/interference
..................................... 15
7.5 Further testing and evaluation . . 15
Annexes
A Example of application using chromatography . 16
B Statistical tests and methods .
..................... 31
C Bibliography . .
..................... 43
0 ISO 1995
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronie or mechanical, including photocopying and
microfilm, without Permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-l 211 Geneve 20 l Switzerland
Printed in Switzerland
ii
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SIST EN ISO 10723:2002
0 ISO ISO 10723:1995(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. Esch 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.
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 ISO 10723 was prepared by Technical Committee
ISO/TC 193, Natura/ gas, Subcommittee SC 1, Analysis of natura/ gas.
Annexes A, B and C of this International Standard are for information only.
. . .
Ill
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SIST EN ISO 10723:2002
0 ISO
ISO 10723:1995(E)
This International Standard describes a method for evaluating the per-
formante of analytical Systems intended for the analysis of natura1 gas.
Natura1 gas is assumed to consist predominantly of methane, with other
saturated hydrocarbons and non-combustible gases.
Performance evaluation makes no assumptions about equipment for
and/or methodology of analysis, but gives test methods which tan be ap-
plied to the Chosen analytical System, including the method, equipment
and Sample handling.
This International Standard contains an informative annex (annex A) which
Shows the application for an on-line gas chromatographic System which,
as described, is assumed to have a response/concentration relationship for
all components which is represented by a straight line through the origin.
lt contains two additional informative annexes (annexes B and C).
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SIST EN ISO 10723:2002
INTERNATIONAL STANDARD 0 ISO ISO 10723:1995(E)
Natura1 gas - Performance evaluation for on-line
analytical Systems
1 Scope
This International Standard specifies a method of determining whether an analytical System for natura1 gas is sat-
isfactory, on the assumptions that
a) the analytical requirement has been clearly and unambiguously defined, for the range and uncertainty of
component concentration measurements, and the uncertainty of properties which may be calculated from
these measurements;
b) the analytical and calibration procedures have been fully described;
c) the method is intended to be applied to gases having compositions which vary over ranges normally found in
transmission and distribution networks.
If the Performance evaluation Shows the System to be unsatisfactory, all the stages, such as
- the analytical requirement;
- the analytical procedure;
- the choice of equipment;
- the choice of calibration gas;
- the calculation procedure;
must be re-examined in the light of the test data to assess where improvements tan be obtained.
This International Standard is applicable to analytical Systems which give the component concentrations and re-
sulting uncertainties. With the present state of knowledge, the method Chosen is likely to be gas chromatography.
Performance evaluation of an analytical System should be performed during installation, then at regular intervals,
according to the application, and/or whenever any critical component of the analytical System is changed or re-
placed.
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 possi-
bility of applying the most recent editions of the Standards indicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
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SIST EN ISO 10723:2002
0 ISO
ISO 10723:1995(E)
Preparation of calibration gas mixtures - Weighing methods.
ISO 6142:1981, Gas analysis -
ISO 6974:1984, Natura1 gas - Determination of hydrogen, inert gases and hydrocarbons up to C8 - Gas chro-
ma tographic me thod.
ISO 6976:1995, Natura/ gas - Cakulation of calorific values, density, relative density and Wobbe index from
composition.
ISO 7504:1984, Gas analysk - Vocabulary.
3 Principle
The analytical System is set up according to the instructions so as to carry out the specified compositional analysis.
The effectiveness of the System is demonstrated by analysing test gases with compositions covering a range
rather wider than that for which the System has been specified.
Test gases prepared according to an appropriate Standard are injected into the analyser to test:
the ability of the System to measure the components specified in the analytical method (System efficiency);
a)
the repeatability of measurement of individual components over their specified ranges;
b)
the relationship between response and concentration of individual components over their specified ranges;
d
the absence of interference between components at different concentration ratios.
d)
The tests required for b) and c) above are conducted over intervals of time comparable with the normal period of
use between regular calibrations. Because a number of Parameters which tan influence the analytical Performance
may vary on a day-to-day basis (barometric pressure variations are a case in Point), it is recommended that the
tests be repeated on at least three separate intervals, so that occasional inconsistencies may be recognized.
However, it is acknowledged that there are circumstances (such as testing analysers installed in remote locations)
where only a Single set of tests tan be obtained.
The results of the tests are analysed to assess analyser Performance with respect to bias, repeatability and inter-
ference. The repeatability test b) Shows the random error associated with the measurement of a component and
whether this varies with concentration. The response function c) Shows the likelihood of bias error arising from
different component concentrations in the calibration Standard and Sample; bias tan also result from component
interference d).
Accuracy of measurement is not included in this list, since analytical accuracy is fundamentally and principally
controlled by the accuracy with which the calibration gas composition is known. The procedures described in this
International Standard allow a judgement as to the ability of the analytical method to provide accurate results if
used with an accurate and appropriate calibration gas.
4 Suitability of analytical Systems
The analytical System to be evaluated shall satisfy the following criteria.
The analytical requirement has been carefully defined, for the range and uncertainty of component concen-
tration measurement, or of physical or Chemical property calculation, or of both.
b) The analytical and calibration procedures, whether manual or automated, laboratory or process, have been fully
described, preferably following appropriate interlaboratory testing. Changes in details of the method are not
permissible during the series of tests. If, at the end of the tests, it is clear that the method fails to provide the
desired Performance, it shall be modified suitably and the entire test procedure reapplied.
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SIST EN ISO 10723:2002
0 ISO ISO 10723:1995(E)
c) The method is not intended to be applied to gases having composition or physical or Chemical properties that
vary over a wider range than would be acceptable for mixing into a normal transmission or distribution System.
Thus, in practical terms, it is unlikely that the concentration will vary for an individual component by more than
a factor of 20, and the Variation for most components,is likely to be less than a factor of 10.
d) The analytical System shall be capable of measuring, either individually or in groups, all components which are
significant for the analytical requirement. Thus, for the measurement of calorific value, nitrogen, carbon diox-
ide, individual hydrocarbons from C, to C, and a composite C,, are commonly required.
When a number of hydrocarbons are identified and quantified as a group or groups, either the total is reported
NOTE 1
as though the group extends from the lowest carbon number of that group (e.g. Cg+, which indicates all hydrocarbons of
carbon number 6 and above), or separate groups may be reported as the total of each carbon number (e.g. total Cg, total
C7, etc.), or further broken down to component types (e.g. CG alkanes, as distinct from benzene and C, cycloalkanes or
naphthenes).
5 Test gases
5.1 Definition
Test gases are mixtures which are used to evaluate the response of the analyser to individual natura1 gas com-
ponents, so that the measured response tan be compared with the assumed one. They may be multi-component
or binar-y mixtures. In all cases, the matrix gas shall be methane, so that the behaviour of the test gases is as
similar as possible to that of natura1 gases. Binary mixtures tan be prepared with smaller uncertainties than
multi-component ones, but more mixtures must be made, one set for each non-methane component to be tested.
Multi-component mixtures allow more repeats to be performed for each component/concentration combination.
Obviously, similar mixtures tan be used to define the response functions of an analyser when it is initially installed,
in which case they shall be referred to as range calibration gases.
NOTE 2 The analytical method may require that the response functions be defined upon installation, or, in the absence of
such a requirement, the user may choose to establish them. Alternatively, the user may rely on the supplier ’s or manufacturer ’s
assumptions about response function, which is usually that the response to all components is represented by a straight line
through the origin. This latter approach is not likely to take full advantage of the potential accuracy of the method.
There is, of course, n 0 poi nt in defining a mo re CO mplex response function if the data handling System available
with the analyser will not f it response data to such a function.
range calibration gases at a particular time (for example, on Day 1) to define the response, yi, of a
Havi ng used
com ponent i in terms of its concentration, Xi, as:
subsequent analyses allow the concentrations of unknown samples to be calculated as
Xi = gi-
’ (Yi>
Rather than redefine the instrument response to each component for each new period of use, the assumption is
usually made that each response function, gi, remains broadly unchanged, but that it needs the minor adjustment
of a scaling, or calibration factor, which is derived from the regular use of a Single calibration gas. This Single cali-
bration gas would invariably be a multi-component mixture, Chosen to have similar component concentrations to
those anticipated in the unknowns. The scaling or calibration factor, a, is defined as
Response to component i in Single calibration gas on Day 1
a, =
Response to component i in Single calibration gas on Day j
and the concentrations of the unknowns are calculated as
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SIST EN ISO 10723:2002
ISO 10723:1995(E)
Xi = Si- ’ (aijmYi>
The frequency with which the Single calibration gas needs to be used is a matter of experience, and instead of
Day 1, we could refer to Hour 1 or Week 1 or Month 1. This frequency shall be defined as part of the analytical
method.
The frequency with which the response function, g, if measured by the User, needs to be re-estab.lished will be
found by applying these test procedures.
From the above, it tan be seen that test gases and range calibration gases could be very similar, if not the Same,
mixtures. When referred to as test gases in this International Standard, they are used to define the up-to-date re-
sponse function, fi which is then compared with the previously established or the assumed function 8.
5.2 Test gas compositions
Test gases shall be Chosen to be suitable for the intended application. However, it is not practicable to make up
test gases which contain all the components in natura1 gas, given the complexity of the higher hydrocarbons which
are commonly found, and the difficulty of preparing high quality mixtures containing condensible components.
or total C, be used. lt is therefore common to use test gases which
Neither tan grouped components, such as C, +
contain only the major components; nitrogen, carbon dioxide, methane, ethane, propane and butane are commonly
used, but any component expected to be present in a concentration greater than 1 % should be included.
Helium, C, and heavier hydrocarbons are usually present at such low concentrations that non-linearity of response
is unlikely to be a Problem. Their repeatability of measurement tan be tested using real natura) gases, ideally with
a range of concentrations appropriate to the application.
The response/concentration relationship shall be tested over the range specified for each component present in
the test gases, and ideally over a slightly greater range. lt is unlikely that a response function more complex than
a third-Order polynomial will be useful and this is satisfactorily defined with seven Points. In those instances where
the range specified for a component is relatively large, it is possible that the repeatability may vary across the
range. For this reason, repeatability testing is carried out with the Same mixtures that are used to evaluate the
response/concentration relationship.
lt is rare that an analyser, however well configured, will measure the sum of components in a natura1 gas to be
exactly 100 %. Consequently, it is common for analysers which have been set up for natura1 gas analysis to nor-
malize the composition data to 100 %, or to some slightly lesser value if there is a small, constant and recognized
contribution from an unmeasured component such as helium. This is based on the obvious premise that a natura1
gas contains 100 % of components, and not some other value. The method should quote limits within which such
normalization would be acceptable; a measured total of between 99 % and 101 % may be deemed to be usual,
with analyses producing wider-ranging totals being rejected. Analytical methods which calculate the methane by
differente do not normalize in this way, but instead forte the total to 100 %, with the calculated methane value
absorbing the errors in all the other component measurements.
Repeatability is influenced by the normalization procedure; normalized data are usually significantly more precise
than unnormalized data. At the same time, normalization allocates the errors involved in the fact that the total does
not resch 100 % or thereabouts between the components pro rata. If the error is produced mainly by one com-
ponent (for example, methane), the normalization process slightly increases the errors for all other components.
This shall be recognized in the procedure. Simplistically, there are two types of error which contribute to totals
other than 100 %, and hence to the need to normalize. The first type affects all components to the Same extent,
and in the case of a gas analyser is typically caused by, among other influences, variations in Sample pressure
within the Sample introduction device. The second type affects components to a different extent, and could be for
example due to random noise, or to variations between the measured and assumed response functions for indi-
vidual components.
The first type tan be compensated for by normalization, but not the second. Furthermore, normalization takes
according to the equation
account of the total calculated composition,
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SIST EN ISO 10723:2002
0 ISO ISO 10723:1995(E)
. .
= Txi = zgr ’ (aijmYi)
Unnormalized total
i=l i=l
Consequently, while it might be interesting to use normalized calculated data, or to normalize raw instrument-
response data according to the calculated unnormalised total, this requires assumptions about the response
function, gi, and the short-term calibration factor, au, which are unlikely to be justified at this Stage. The test gases
should be used in circumstances which minimize errors of the first type, such as shutting off the Sample flow
before introduction of the Sample. Only unnormalized data should be used for these tests.
Esch component shall be tested at seven values of concentration. These shall be, so far as possible, equally
spaced across the specified range, and also covering one Point below and one Point above the range. If the lowest
and highest concentrations specified are xL % and xU %, the mixtures should contain:
Mixture Concentration (%)
1 xL - 0,25 (x, - xL)
2
XL
xL + 0,25 (x, - xL)
3
$ + 0,5 (x, - XL)
4
5 XL + 0,75 (X” - XL)
6
Tl
7 xu + 0,25 (x, - xL)
Achieving these exact values may not always be possible, in which case the nearest practicable concentration
10, the concentration value for mixture 1 would be negative, and so a
should be the aim. Thus if xL = 1 and xu =
value of (0,5x,) % may be Chosen. If xL = 0, mixture 1 may be Chosen to be near the limit of detection, and mixture
2 to be between this value and mixture 3. Similar Problems may occur for methane. The uncertainty with which
these target concentrations are met should be not greater than &- 0,l (xu - xL) %. The uncertainty relating to
knowledge of the exact concentrations achieved should, of course, be significantly smaller than this.
Where multi-component mixtures are to be used, it is unlikely that each one tan be formulated to have a com-
Position similar to that of an anticipated Sample gas, and particular mixtures may contain more propane than
ethane, for example. However methane will always be the major component.
These mixtures shall be prepared or certified by a method whose Overall uncertainty is not greater than that
specified for the analytical System under test, and preferably rather less.
6 Test procedures
6.1 System efficiency test
The analytical System shall be capable of measuring each component for which the method has been specified,
over the expected range of concentrations. lt shall not give false indications for any other components not speci-
fied in the analytical requirement, but which may reasonably be expected to be occasional contaminants in a
Sample. Furthermore, the System should not give any response for specified components in their absence.
The ability of the method to cope with the specified components shall be assessed by analysis of Standard gases
which have been prepared to contain these components at appropriate levels, or of natura1 gases the compositions
of which have been defined by comparison with such Standards. Exact quantitative accuracy is not needed here,
so the methods of preparation may be selected for Speed or convenience.
If the method is configured in such a way that one or more groups of components are measured as a Single
“pseudo-component” or series of “pseudo-components ”, the correct allocation of components to these groups
shall be checked. A typical example would be a recombined (e.g. backflushed) C,, group, consisting of all C, and
5
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SIST EN ISO 10723:2002
ISO 10723:1995(E) 0 ISO
heavier hydrocarbons. The timing of the backflushing Operation shall not allow any C, or heavier components to
fail to be included, nor C, or lighter components to be grouped where they should not be .
The approach to the presence of contaminants in a Sample will vary according to whether or not remedial action
is required. Air is a common contaminant if samples are taken’ for laboratory analysis, and tan be recognized by
the presence of Oxygen. Usually, an analytical method will permit the composition to be recalculated on an air-free
basis, provided that the concentration of air is below a defined value. In this case, the Oxygen shall be measured
with high accuracy, since the adjustment for a given observed amount of Oxygen involves the removal of a cal-
culated amount of nitrogen which is about four times larger. On the other hand, in particular circumstances other
components may be expected to be present at concentrations comparable to those of the C, or C, hydrocarbons,
but their measurement is not required for the purpose for which the analysis is performed. In this case, it shall
be established whether or not the contaminant interferes with measurement of any of the expected components,
and if so, how large an effect is Seen.
Any response for a component in its absence tan be tested by a blank experiment, which simulates all the ac-
tivities of the analytical System. Thus, in the case of a chromatographic method, injection of carrier gas instead
of Sample gas would be appropriate.
Any detecta ble response at this Stage should, if possible, be eliminated by suitable adjustment of the method.
Otherwise, it will impose a fixed bias error on the response/concentration relationship.
6.2 Repeatability
Repeatability is often measured as that of instrument response; the Standard deviation of peak area counts in the
case of a chromatographic method. This measurement cannot be used in isolation for two reasons. The mean and
Standard deviation of a normally distributed (Gaussian) set of data are measures such that 67 % of all the data
Points lie within + 1 Standard deviation of the mean; thus, while the Standard deviation is a convenient measure
-
to use while assessing error contributions, it shall be converted at the end of the calculations to a value which
more nearly describes what we understand by repeatability (see clause 8.4). Also, a typical analytical result is de-
rived using a relationship of the type
& = y;td x -%td
is the concentration in unknown (Sample);
%
is the response to unknown (Sample);
Ys
is the response to Standard;
%td
is the concentration in Standard.
Ystd
Consequently, the repeatability of the result is influenced by the repeatability of both the unknown and of the
Standard. Uncertainty associated with the calibration gas Standard also contributes, but is outside the scope of this
International Standard. The evaluation procedure assesses the ability of the analytical System to provide high
quality data, if used with a calibration Standard which has a weil-known composition and is appropriate for the
application. The quality of such calibration Standards is properly dealt with in other International Standards.
The repeatability of measurement of a component may be uniform over the expected concentration range, or it
may vary as a function of concentration. Figure 1 illustrates the
...
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