ISO/TR 13530:1997

ISOITR
TECHNICAL
13530
REPORT
First edition
1997-09-01
Guide to analytical quality
Water quality -
control for water analysis
Guide de contr6le qua/it& analytique pour I’analyse de
Qua/it6 de I’eau -
I’ea u
IN ADDITION TO THEIR EVALUATION AS
FOR INDUSTRIAL,
BEING ACCEPTABLE
TECHNOLOGICAL, COMMERCIAL AND USER
=--
PURPOSES, DRAFT INTERNATIONAL STAND-
ARDS MAY ON OCCASION HAVE TO BE
CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
Reference number
WHICH REFERENCE MAY BE MADE IN
ISOnR 13530:1997(E)
NATIONAL REGULATIONS.

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ISO/TR 13530: 1997(E)
Contents Page
..................................................................................................
1 Scope 1
2 Normative references . 3
3 The nature and sources of analytical errors . 3
4 The quality system in water analysis . 6
5 Performance characteristics of analytical systems . 15
6 Specifying analytical requirements for water analysis . 17
7 Choosing analytical systems . 19
Initial tests to establish performance of analytical system . 24
8
9 Intralaboratory quality control . 33
..................................................................
10 Quality control in sampling 42
11 Interlaboratory quality control . 44
Quality control for lengthy analytical procedures .
12 46
Annexes
Evaluation of interference effects on analytical methods . 48
A
B Recovery of all forms of the determinand . 56
.........................................................
C Cali bration and blank correction 58
D .
Sample stability 63
E Bibliography . 70
0 IS0 1997
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Internet central @ iso.ch
x.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
ii

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ISOnR 13530:1997(E)
@ IS0
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
technical committees. Each member body interested in a subject for which
a technical committee has been established has the right to be represented
on that committee. International organizations, governmental and non-
governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
The main task of technical committees is to prepare International
Standards, but in exceptional circumstances a technical committee may
propose the publication of a Technical Report of one of the following types:
- type 1, when the required support cannot be obtained for the
publication of an International Standard, despite repeated efforts;
- type 2, when the subject is still under technical development or where
for any other reason there is the future but not immediate possibility of
an agreement on an International Standard;
- type 3, when a technical committee has collected data of a different
kind from that which is normally published as an International Standard
(“state of the art”, for example).
Technical Reports of types 1 and 2 are subject to review within three years
of publication, to decide whether they can be transformed into International
Standards. Technical Reports of type 3 do not necessarily have to be
reviewed until the data they provide are considered to be no longer valid or
useful.
ISO/TR 13530, which is a Technical Report of type 2, was prepared by
Technical Committee ISOnC 147, Water quality, Subcommittee SC 7,
Precision and accuracy.
This document is being issued in the Technical Report (type 2) series of
publications (according to subclause G.6.2.2 of part 1 of the ISO/IEC
Directives, 1995) as a “prospective standard for provisional application” in
the field of water quality because there is an urgent need for guidance on
how standards in this field should be used to meet an identified need.
This document is not to be regarded as an “International Standard”. It is
proposed for provisional application so that information and experience of
its use in practice may be gathered. Comments on the content of this
document should be sent to the IS0 Central Secretariat.
A review of this Technical Report (type 2) will be carried out not later than
three years after its publication with the options of: extension for another
three years; conversion into an International Standard; or withdrawal.
Annexes A to E of this Technical Report are for information only.
. . .
III

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~~~
ISO/TR 13530:1997(E)
TECHNICAL REPORT @ IS0
Guide to analytical quality control for water
Water quality -
analysis
1 Scope
This Technical Report (type 2) is a guide with the objective of providing detailed and comprehensive
guidance on a coordinated programme of within-laboratory and between-laboratory quality control for
ensuring the achievement of results of adequate and specified accuracy in the analysis of waters and
associated materials.
This Technical Report and its annexes are applicable to the chemical and physicochemical analysis of
natural waters (including sea water), waste water, raw water intended for the production of potable
water, and potable water. It is not intended for application to the analysis of sludges and sediments
(although many of its general principles are applicable to such analysis) and it does not address the
biological or microbiological examination of water. Whilst sampling is an important aspect, this is only
briefly considered. I
Analytical quality control as described in this Technical Report is intended for application to water
analysis carried out within a quality assurance programme. This Technical Report does not address the
detailed requirements of quality assurance for water analysis.
The recommendations of this Technical Report are in agreement with the recommendations of
established quality assurance documentation (for example IS0 Guide 25 and EN 45001). A discussion of
quality systems in water analysis is provided in clause 4 to set in context the recommendations on
quality control.
This Technical Report is applicable to the use of all analytical methods within its field of application,
although its detailed recommendations may require interpretation and adaptation to deal with certain
types of determinand (for example non-specific determinands such as suspended solids or biochemical
oxygen demand). In the event of any disparity between the recommendations of this Technical Report
and the requirements of a standard method of analysis, the requirements of the method should prevail.
The basis of the Technical Report is to ensure the achievement of results of adequate accuracy by
adherence to the sequential stages of analytical quality control shown in figure 1.
1

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ISOITR 13530:1997(E)
Purpose
Activity
To plan and coordinate subsequent activity.
Establish working
group
Define analytical To ensure clear specification of analytical require-
ments.
objectives
I
. .
To select methods/systems capable of the required 2 ”
Choose analytical
1 methods/systems 1) accuracy.
4. To ensure that the chosen methods are followed
Ensure unambiguous
description of methods properly.
I I
5. Estimate To ensure that each laboratory achi.eves adequate
within-laboratory precision and to check certain sources of bias.
precision and spiking
recovery
Ensure accuracy of To etiminate this source of bias in each t’aboratolry
standard solutions. and to prepare fuE& more detailed bias checks.
Preliminary check on
interla boratory bias
Set up quality control
To maintain, a continuing check on analytical perfor-
* charts mance in each laboratory.
Undertake tests of To ensure that each laboratory achieves adequately
interlaboratory checks
small errors.
To ensure long-term control of the accuracy and-
accuracy using control
comparability of analytical results.
’ charts and regular
interlaboratory tests
Figure 1: Sequence of activity for analytical quality control
1) The analytical method is the set of written instructions followed by the analyst. The analytical system includes all
aspects of producing results, i.e. method, equipment, analyst, laboratory environment, etc.

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CSOflR13530:1997( E)
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions
of this Technical Report. At the time of publication, the edition indicated was valid. All standards are
subject to revision, and parties to agreements based on this Technical Report are encouraged to
investigate the possibility of applying the most recent editions of the standards indicated below.
Members of IEC and IS0 maintain registers of currently valid International Standards.
IS0 5667-l : 1980, Water quality - Sampling - Part 7: Guidance on the design of sampling programmes
IS0 5667-2:1991, Water quality - Sampling - Part 2: Guidance onsampling techniques
IS0 5667-3:1994, Water qualify - Sampling - Part 3: Guidance on the preservation and handling of
samples
IS0 8466-l: 1990, Water quality - Calibration and evaluation of analytical methods and estimation of
performance characteristics - Part 7: Statistical evaluation of the linear calibration function
IS0 8466-2:1993, Water quality - Calibration and evaluation of analytical methods and estimation of
performance characteristics - Part 2: Calibration strategy for non-linear second order ,calibration
IS0 Guide 25: 1990, General requirements for the competence of calibration and testing laboratories
. EN 45001:1989, General criteria for the operation of testing laboratories
3 The nature and sources of analytical errors
3.1 General
The following clauses provide a succinct discussion of the nature and origin of errors in analytical
results for waters and effluents. Further information on many of the topics covered is given elsewhere
in this Technical Report, and the subject is also discussed extensively in.[18].
3.2 Nature of errors
The results of chemical analysis of waters and effluents (like those of all measurement processes) are
subject to error, i.e. the measured concentrations differ from the true concentrations.
3.2.1 Total error
The total error, E, of an analytical result, R, is defined as the difference between that result and the true
value, T; i.e.
E= R-T
As the total error decreases, the accuracy of the result is said to increase.
In general, the total error represents the sum of random error and systematic error.
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,ISO/TR 13530: 1997(E)
3.2.2 Random error
Repeated analysis of identical portions of the same, homogeneous sample does not, in general, lead to
a series of identical resultsz). Rather, the results are scattered about some central value. The scatter is
attributed to random error, so called because the sign and magnitude of the error of any particular
result vary at random and cannot be predicted exactly. Precision is said to improve as the scatter
becomes smaller - i.e. as random error decreases - and imprecision is therefore a synonym for random
error.
Because random errors are always present in analytical results, statistical techniques are necessary if
correct inferences regarding true values are to be made from the results.
Terms such as “repeatability” and “reproducibilty” have specialized meanings in the context of
interlaboratory collaborative trials. In this Technical Report, random error is quantified in terms of the
standard deviation, cx Since exact measurement of the standard deviation generally requires an infinite
number of repeated results, only estimates, s, of owill usually be obtainable. The number of degrees of
freedom (DF) of the estimate provides an indication of its worth; as the number of degrees of freedom
increases, the random error of the estimate itself, s, decreases.
3.2.3 Systematic error
Systematic error (or bias) is present when there is a persistent tendency for results to be greater, or
smaller, than the true value. The mean of n analytical results for identical portions of a stable, homoge-
neous sample approaches a definite, limiting value, p, as n is increased indefinitely. When p differs
from the true value, T, results are said to be subject to systematic error or bias, 8, where:
/3=p-T
Because an indefinitely large number of determinations cannot be made on a single sample, the effect
of random error prevents exact determination of p, and hence also of 8. Only an estimate, X, of p will
generally be available, so that only an estimate, b, of /3 can be obtained.
As the systematic error or bias of results decreases, trueness is said to increase.
3.3 Sources of error
The distinction between random and systematic errors is important for two reasons: first, because they
have different effects on the use to be made of analytical results, and second, because they usually
have different origins.
Causes of random error
3.3.1
Random errors arise from uncontrolled variations in the conditions of the analytical system 3) during
different analyses. The nature of such variations include, for example, differences in the volume of
sample or reagent taken on different occasions, fluctuations in temperature - either in time, or across
the different sample positions in a heating bath, block or oven, fluctuations in instrumental conditions
(for example in temperatures, fluid flowrates, voltages and wavelengths) and operator-induced
variations in reading scales. Variations from batch to batch, in the extent to which the calibration
function represents the true calibration for that batch, also give rise to between-batch random errors,
whereas a consistent calibration error across many batches gives rise to systematic error - see below.
This may not be true when the discrimination of the analytical system is coarse. However, the apparent perfect
2)
concordance of repeated results in such a situation is illusory, because samples differing in concentration will also
give the same results.
The analytical system is the combination
of all factors - analyst, equipment, method, reagents, etc. involved in
producing analytical results from samples.
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ISOPTR 13530:1997(E)
Whilst many of these factors causing random errors can be more closely controlled to achieve better
precision, they can never be totally eliminated, so that all results are subject to some-degree of random
error.
3.3.2 Causes of systematic error
There are five general sources of systematic error (if clear blunders by the analyst in carrying out the
written method, and bias introduced by the sample collection itself are both excluded). .
These are:
Instability of samples between sample collection and analysis
a)
This is a potentially important source of error in many cases, and evidence should
always be obtained - either from the literature or by direct test - to ensure that
unacceptable bias is not introduced by this factor. Effective sample stabilization
procedures are available for many determinands, but they should be compatible with
the analytical system being employed, and with the particular sample type being
analysed.
Inability to determine all relevant forms of the determinand
b)
Many substances exist in water in a variety of physical and/or chemical forms (or
“species”). For example, iron can exist in both dissolved and particulate forms, and
within each of those physical categories a variety of chemical species may be present -
for example free ions and complexes, including those of different oxidation states, in
the dissolved phase. An inability of the analytical system to determine some of the
forms of interest will give rise to a bias when those forms are present in samples.
Some determinands are overall properties of a sample, rather than a particular
substance - for example biochemical oxygen demand (BOD). Such determinands are
called “non-specific” and have to be carefully defined by specifying the use of a
particular analytical method. The so-called “dissolved’ fractions of, for example trace
metals, are also non-specific in the sense that the type and pore-size of filter toe be used
in their determination should be clearly specified.
Interferences
d
Few analytical methods are completely specific for the determinand. Response to
another substance (for example, response to iron by a spectrophotometric procedure
for manganese based on formaldoxime) will give rise to biased results substance is present in samples, and it is important that the effects of all such
intetferents likely to be present in samples are known before a new method is applied
routinely.
In some cases, the effect of another substance is to alter the chemical state of the
determinand such that it is not measured by the method being used - for example, the
presence of fluoride will cause aluminium complexes to form, which may not be
measured by an ion-selective electrode. Such an effect can be regarded as an
interference upon the determination of total dissolved aluminium, or as a failure to
recover all forms of dissolved aluminium. Although it more strictly falls into the latter
category, the effect - and others like it - may be most conveniently treated as an
interference when data on performance characteristics are being obtained or reported
(see clause 5 and annex A).
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ISOmR 13!S30:1997(E)
Biased calibration
d)
Most methods require the use of a calibration function (explicit or implicit) to convert
the primary analytical response for a sample to the corresponding determinand
concentration. If the samples and calibration standards are treated in exactly the same
manner (and provided that the materials used to prepare the calibration standards are
of adequate purity) no systematic error should arise from the calibration” (It has been
noted in 3.3.1 that any variations in the correctness of the calibration from batch to
batch will be manifested as between-batch random errors).
If, however, samples and calibration standards are treated differently, this can
represent a p.otentially serious source of error. Thus, for example, a method
prescribin.g some form of pre-concentration of the determinand from samples, but
employing direct calibration with standa$rds not taken through the pre-concentration
step, will give rise to negative bias if the’ pre-concentration recovery is less than 100 %.
In such cases, evidence should be obtained on the accuracy of the prescribed
calibration, or the difference in treatment of samples and standards eliminated.
Impurity of the material used to prepare calibration standards is, of course, another
potential cause of biased results.
Biased blank
d
The same considerations as in d] above appb to b&~~+ks, There isE, Hoover, another
source of bias arising f&m bllank correction, !f the water used for the bEank c.ontaEns the
determinand, results for samples wiEB be biased I&M by a,n equi&&nt an~unt W&SS a
correction for the determinand content of the blank water is a.pplied, ldealLy~ howe~er,~ a
source of blank water should be obtained, su.ck that, the: determinand emtent is
negligible in comparison with the concentration in s;~mpIes.
4 The quality system in water analysis
4.1 General
The quality system is the term used to describe the aspects which are intended to meet the clients’
requirements. The control of analytical errors, usually termed analytical quality control (AQC) is an
important component of the quality system. This clause summarizes the key issues which should be
addressed in designing a quality system.
For more detail and an authoritative account of quality assurance, readers should consult the standards
listed in clause 2, together with documentation provided by the various national accreditation bodies.
4.2 Quality system
4.2.1 .Aims and form of quality system
The laboratory should operate a quality system appropriate to the type, range, precision and volume of
tests that it undertakes. The quality system should be such as to ensure that the requirements of this
Technical Report are fully met on a continuing basis. All staff should be made fully aware of, and be
required to comply with, the documented quality system.
The ‘laboratory should possess a statement of the aims and general form of the laboratory’s quality
system, including the purpose of the quality manual and associated documentation.
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@ IS0 ISO/TR 13530: 1997(E)
4.2.2 Quality manual
The quality system should be formalized in a quality manual which should be maintained and kept up-
to-date.
The person responsible for authorization and compilation of the quality manual should be identified. A
distribution list of the quality manual and identification of holders of controlled copies of the quality
manual should be included.
The quality manual should contain, for example the following items or equivalent:
1 Scope.
2 References.
3 Definitions.
4 Organization and management.
5 Quality system, audit and review.
Personnel.
6
7 Accommodation and environment.
Equipment and reference material.
8
9 Measurement, traceability and calibration.
10 Test methods.
Handling of calibration and test items.
11
Records.
12
Certificates and reports.
13
14 Subcontracting of calibration or testing.
Outside support services and supplies.
15
16 Complaints.
4.2.3 Quality management
The quality system should include a statement of the responsibilities and authority of the technical
manager and quality manager, and any appointed deputies.
The quality system should include a statement of the general arrangements for implementing each of
the quality manager’s and deputy’s responsibilities and the specific procedures for implementing these
responsibilities, or identification of laboratory documents containing such procedures.
4.2.4 Documentation
The quality system should include a statement of the quality manager’s responsibility in relation to
control and maintenance of documentation, including the quality manual, and of the specific
procedures for control, distribution, amendment, updating, retrieval, review and approval of all
documentation relating to the testing work of the laboratory.
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It should be made clear that laboratory staff should have ready access to all documentation, including
the quality manual test procedures, and all relevant standard specifications.
There should be an instruction forbidding alteration of laboratory documentation, except under
Instructions should also require adherence by all staff to the
conditions specified by management.
laboratory’s laid-down policies and procedures, except under clearly specified conditions.
The instruction should indicate clearly the circumstances under which departures from documented
policies and procedures or standard specifications are permitted. It should also indicate that departures
should be endorsed by management and their justification included in relevant records.
The quality system should include a statement of the specific procedures for dealing with situations
where staff have not followed documented policies, procedures and standard specifications as
required.
4.3 Quality policy
4.3.1 Management statement
The quality system should include a statement by senior management of the policy of the laboratory as
regards quality in all aspects of its work.
4.3.2 Quality systems
The quality system should include a statement of the intentions of the laboratory management
relation to q uality of service.
The quality system should include a statement that it is the responsibility of all staff to familiarize
themselves with the content of the quality manual and to comply with the policies and procedures laid
down in the quality manual and associated documentation.
These statements should be made on the authority of a senior executive, who has direct management
responsibility for the laboratory and who is at the highest level of management on which decisions are
taken on laboratory policy and resources. They should be authenticated by the signature, and legible
name and position, of the person concerned.
The policy statements should indicate:
- title of the person responsible for implementing the quality policy in the laboratory,
- title of the person having overall responsibility for control of quality and who advises on and monitors
all aspects of quality in the laboratory.
4.4 Organization and management
4.4.1 Organization
The quality system should include a statement to the identity and legal status of the laboratory
(including ownership and corporate position in relation to any parent organization or grouping of
companies) and a statement of the technical role of the laboratory (for example independent,
commercial, calibration/testing, or product quality control in support of a particular manufacturer).
A brief historical background should be included which is relevant to the standing of the laboratory,
together with a summary of the scope of operation and range of testing performed by the laboratory
and an inventory of tests performed by the laboratory.

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ISWTR~ 13530: 1997(E)
4.4.2 Organization charts
Organization charts should be used showing:
technical manager, quality manager, and any deputies;
general lines of responsibility within the laboratory (including the relationship between
management, technical operations, quality control and support services);
the lines of responsibility within individual sections of the laboratory;
the relationship between the laboratory and any parent or sister organizations.
The appropriate chart should show that, for matters related to quality, the quality manager has direct
access to the highest level of management at which decisions are taken on laboratory policy or
resources, and to the technical manager.
4.4.3 Management
Details of job descriptions, qualifications, training and experience should be provided for:
technical manager;
quality manager;
other key laboratory managerial and technical posts.
Job descriptions should include:
title of job and brief summary of function;
person or functions to whom jobholder reports;
person or functions that report to jobholder;
key tasks that jobholder performs in the laboratory;
limits of authority and responsibility.
Technical manager - the quality system should include a statement that the post-holder has overall
responsibility for the technical operation of the laboratory and for ensuring that the quality system
requirements are met.
Quality manager - the quality system should include a statement that the post-holder has responsibility
for ensuring that the requirements for the quality system are met on a day-to-day basis and that the
post-holder has direct access to the highest level of management at which decisions are taken on
laboratory policy or resources, and to the technical manager.
The quality system should include a statement of:
any special arrangements for management and other functions, in the event of the
absence of key staff;
method whereby the laboratory makes all staff aware of the extent and limitations of
their responsibility;
laboratory policy with respect to influences or inducements that might adversely affect
the judgement of staff or the result of their work;

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ISO/TR 13530: 1997(E)
actions to be taken by staff on encountering such influences or inducements;
policy and general arrangements for en suring the protection of proprietary
laboratory
of site security.
rights and information, and for other aspects
4.4.4 Staff qualifications and training
The quality system should include a statement of the laboratory’s general criteria for engagement of
staff and their assignment to respective duties and list the relevant academic and/or professional
qualifications, training and experience of key managerial, technical and other staff.
the laboratory’s procedures for defining in writing
The q uality system shou which ~ members of staff are authorized to use equip Iment or perform specific calib
...