ISO 8466-1:2021

INTERNATIONAL ISO
STANDARD 8466-1
Second edition
2021-11
Water quality — Calibration and
evaluation of analytical methods —
Part 1:
Linear calibration function
Qualité de l'eau — Étalonnage et évaluation des méthodes
d'analyse —
Partie 1: Fonction linéaire d'étalonnage
Reference number
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Determination of the linear working range and establishment of the calibration
range . 4
5.1 General . 4
5.2 Preliminary choice of working range . 4
5.3 Estimation of the linear working range . 4
5.3.1 General . 4
5.3.2 Visual testing of measurement data — Testing using the x/y-diagram. 5
5.3.3 Estimation of the linear range by calculating the point-to-point slope . 5
6 Calibration strategies .6
6.1 General . 6
6.2 Calculation of the calibration function . 8
6.3 Calibration of the measuring method using an external standard, including
determination of the recovery rate of the analyte . 9
6.3.1 General . 9
6.3.2 Establishing the calibration function . 9
6.3.3 Determination of the recovery rate . 10
6.3.4 Calculation of results . 10
6.4 Calibration of the measuring method using an internal standard, including
determination of the recovery rate of the internal standard . 11
6.4.1 General . 11
6.4.2 Establishing the calibration function . 11
6.4.3 Determination of the recovery rate . 11
6.4.4 Calculation of results .12
6.5 Calibration of the total procedure using an external standard .12
6.5.1 General .12
6.5.2 Establishing the calibration function .12
6.5.3 Calculation of results .13
6.6 Calibration of the total procedure using an internal standard .13
6.6.1 General .13
6.6.2 Establishing the calibration function . 13
6.6.3 Calculation of results . 14
6.7 Standard addition . 14
6.7.1 General . 14
6.7.2 Procedure . 14
6.7.3 Calculation of results .15
7 Strategies for testing the validity of calibration .16
7.1 General . 16
7.2 Testing by means of a control solution or control sample . 16
7.3 Testing the slope of the calibration line . 16
Annex A (informative) Goodness-of-fit test according to Mandel, standard deviation of the
procedure, variation coefficient of the procedure and confidence interval .17
Annex B (informative) Examples of linearity testing .20
Annex C (normative) Examination of the linear working range using the empirical test of
curvature .32
iii
Annex D (informative) Weighted regression — Weighting 1/x .39
Bibliography .41
iv
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 (see 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 (see 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 of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2,
Physical, chemical and biochemical methods.
This second edition cancels and replaces the first edition (ISO 8466-1:1990), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the title has been modified;
— the scope of the document is the calibration for routine analysis;
— calculation of performance characteristics has been moved to the informative Annex A;
— the calibration range has been extended to several decade orders of magnitudes;
— the verification of the homogeneity of variances has been deleted;
— the linearity test has been modified;
— various calibration strategies have been described;
— the document has been editorially revised.
A list of all parts in the ISO 8466 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
Introduction
Calibration is a prerequisite for the quantification of analytes by means of physicochemical and
chemical methods. In most cases, simple linear regression is applied because many measuring methods
show a linear relationship between the indicated value and the sample content.
Since the publication of ISO 8466-1 in 1990, a huge progress has been made in the field of instrumental
analysis, a consequence of which is that various calibration strategies have been developed in order to
make best use of the equipment. The calibration range of many analytical methods was constrained to
a maximum of one order of magnitude by the theoretical statistical requirement to only apply simple
linear regression if homogeneity of variances exists across the selected working range. Due to the
estimation of measurement uncertainty by calculation of the confidence interval in ISO 8466-1:1990, it
had been necessary to conform to the required homogeneity of variances. Meanwhile, other methods for
the estimation of measurement uncertainty that are independent of calibration have been established
(e.g. ISO 11352).
Calibration is always done in two steps. The first step comprises the determination of the linear
range, the second step is the calculation of the calibration function. The calibration strategies that are
described in this document enable the analyst to individually define the calibration effort according
to specified requirements. The method that is described in ISO 8466-1:1990 remains part of the
informative annex since it can still be useful for specific purposes (e.g
...