CEN Guide 13:2008

SLOVENSKI STANDARD
01-junij-2009
Validacija okoljskih preskusnih metod
Validation of environmental test methods
Ta slovenski standard je istoveten z: CEN Guide 13:2008
ICS:
19.040 Preskušanje v zvezi z Environmental testing
okoljem
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN
GUIDE
Validation of environmental
test methods
Version dated 2008-10-29
CEN Guide 13 Validation of environmental test methods

Contents
Contents .2
Foreword.3
Introduction.4
1 Scope.7
2 Validation of reference methods.8
2.1 General.8
2.2 Validation of the whole measurement process .10
2.3 Validation of the sampling steps .11
2.4 First step of validation (robustness testing).12
2.5 Second step of validation (interlaboratory testing – repeatability – reproducibility).14
2.6 Final draft standard.14
3 Validation of alternative methods.16
4 Validation of guidelines .17
5 Validation of non-experimental methods.18
Annex: Explanations of terms used in this document .19
References – Bibliography .21

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CEN Guide 13 Validation of environmental test methods

validation tasks interacts with the elaboration of the
draft standards, and so there is also a general need
Foreword
to document the performed validation tasks and their
results in the standard.
This document has been produced by the CEN-
This document focuses on the validation tasks in the
SABE Environmental TCs Cooperation Team (ENV
standardisation process of reference methods, being
TCs) as a policy document on validation tasks in
either the whole measurement process or one of its
the standardisation process of environmental
constituent parts.
test methods.
The environmental TCs recognise that these

Decision of TC
validation tasks are complex. They consist of two
to start a New
Work Item
main steps, the robustness testing and the inter-
Experts
laboratory testing (determining repeatability and meetings in
CEN/TC/WG
reproducibility), both interacting with the elaboration

draft standard
of the draft standards as shown in the flow chart.

based on experts
Furthermore, they apply to the different inter-related
opinions
Robustness
phases of encountered in environmental testing,
testing by
expert
typically sampling and production of laboratory
laboratory
revised draft
sample, storage and transportation, extraction,
standard based on
results robustness
analysis and reporting. Consequently, this document
testing
focuses on the ‘why’ and ‘what’ of validation tasks in

Interlaboratory
direct relation to the different steps of the standardi-
testing
prEN standard
sation process. Given the policy aim of this
based on
document, it does not contain detailed procedures repeatability and
reproducibility
for performing the validation (such as number of
testing
laboratories, number of samples, etc.).
Publication as
The environmental TCs recognise that the
EN standard ?
environmental test methods published as standards

Decision of TC
are very often used as reference methods in

to launch the
regulations and/or in contracts between several CEN enquiry

parties. Therefore, a known quality is considered

as vital prior to publishing an environmental test Flow chart of the validation tasks in the standardisa-
tion process
method as a standard. Hence a general need for
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CEN Guide 13 Validation of environmental test methods

Introduction
View of the Environmental TCs on validation
This paper is intended by the CEN-SABE Environmental TCs Cooperation Team to be a policy document on
validation. It defines the view of the Environmental TCs on the role of validation in the process of the
standardisation of environmental test methods.
Consequently, this document focuses on the ‘why’ and ‘what’ of validation in direct relation to the different steps
of the standardisation process. Given the policy aim of the document, this document does not contain detailed
procedures for performing the validation (such as number of laboratories, number of samples, etc.).
Uncertainty
The tests results in the environmental fields are often applied for the enforcement of regulation or for contract
execution. In such legal situations it is vital that the associated uncertainties in the tests' results are known.
The relation between the test result (TR) and the uncertainty (U) is generally presented as TR ± U. When the
regulatory or contractual limit value is above TR + U or below TR – U, the conclusion is clear, respectively
fulfilling or exceeding the limit value. If the limit value lies between these two boundaries, it is not possible to
come to a clear conclusion.
This is an even bigger problem when the associated uncertainty is unknown, as, despite the test result itself, it is
impossible to ascertain that the test result is really above or below the limit value.
Validation of an environmental test method is aimed at providing sound information on the uncertainty of the
tests' results, and by that means, providing the possibility to come to sound conclusions based on the
standardised measurements (see in bibliography the IPPC-REF document on monitoring).
Request from CEN/SABE
Resolution 26/2004 of SABE taken on 19 October 2004 invites all environmental TCs to establish their own policy
regarding the publication of validated or non-validated standards. The environmental TCs agreed that a
commonly developed policy on validation would be preferable, therefore giving the lead for the development of
this policy statement to the Environmental TC Cooperation Team.
In relation to its request, SABE wished to highlight two issues:
• there may be a financial liability if action is taken on the basis of a CEN document, and as such the
uncertainty of the test result should be known;
• the subject of uncertainty influences the credibility of CEN.
Indeed, these two points are fully recognised by the environmental TCs.
Views within CEN
Uncertainty: 'A parameter, associated with the result of a measurement that characterises the dispersion of
the values that could reasonably be attributed to the measurand' (VIM and GUM).
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CEN Guide 13 Validation of environmental test methods

When developing a policy view on validation, benefit should be taken of already established policies on validation
within other CEN-sectors.
In general, the common view is that a test method can only be published as an EN when fully validated (first and
second validation steps have been performed). It may happen that the results are considered by the WG expert
as very poor and that they recommend to the TC to publish a TS instead. When no or only partial (e.g. first step)
validation results are available at the time of completion of the CEN enquiry, the test method is to be published as
a Technical Specification (TS).
When (partial) validation has been performed, the resulting performance characteristics are to be included in a
separate section of the test method (specific clause or annex performance characteristics).
Consideration should be given to ENV 13005 Guide on Uncertainty in Measurement (GUM). It is to be noted in
EN-ISO 17025 that 'General requirements for the competence of testing and calibration laboratories' requires that
laboratories provide results with the associated uncertainties.
Major impact
There are different interpretations of the term ‘validation’, even within the environmental fields. However, there is
a consensus that ‘validation’ is a key step in the standardisation process of environmental tests' methods.
Consequently, the definition of the term ‘validation’ has a major impact on the quality of the standards that
describe a test method.
Defining a common policy on validation within the environmental sector of CEN also has, in turn, an impact on
the work of the environmental TCs.
General principle within the environmental sector
The previously mentioned common view within CEN is embraced by the environmental TCs. This implies that
only validated test methods can be published as EN standards. Test methods that are not or only partly validated
are to be published as TSs. At the same time, the environmental TCs recognise the fact that not all standards are
indeed test methods and, therefore, there might be a necessity to differentiate this general principle to some
extent.
This policy document aims to clarify in which situations validation is to be considered as essential, and in which
cases it is of less or of no importance. In addition, the validation activities during the different steps of the
standardisation process are clarified.
Whenever there is a deviation from the general principle to publish validated standards, this should be a
conscious decision of the involved TC.
Validation of the whole measurement process
For the user / the customer of a standard or a series of standards, the reliability of the final overall result of a test
is of major importance. That is the reliability that is obtained through all steps of the measurement process.
Consequently, validation should not be just aimed at a single step of that procedure (like the analysis), but indeed
should be aimed at quantifying the uncertainty that is associated with the full test procedure.
Depending on the matrix and the components that are to be assessed, this whole measurement process can be
relatively simple or very complex. At least for part of the measurements in the environmental field, the whole

i.e. sampling plan, taking of sample, sample pre-treatment in the field, packaging, storage and
transportation, storage and conservation, sample pre-treatment, extraction, destruction, leaching, clean-up,
analysis / quantification, data management, report
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measurement process involving the appliance of a series of standards and full validation of the whole
measurement process is not that simple. Therefore, this document starts with the validation of the individual
steps of the whole measurement process, like the analytical determination of the content, and only after that will
look at the validation of the whole measurement process.
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CEN Guide 13 Validation of environmental test methods

1 Scope
This document provides guidance on the validation tasks in the standardisation process of environmental
test methods.
It deals with the two main steps of such validation tasks, the robustness testing and the interlaboratory testing
(determining the repeatability and reproducibility), both interacting with the elaboration of the draft standards as
shown in the flow chart given in clause 2.1. It applies to the different inter-related phases of the environmental
test methods, typically sampling and the production of a laboratory sample, storage and transportation of the
laboratory sample, extraction, analysis or quantification of a test portion and finally reporting. Consequently, this
document focuses on the ‘why’ and ‘what’ of validation tasks in direct relation to the different steps of the
standardisation process. This document is focussed on the validation tasks in the standardisation process of
reference methods either for the whole measurement process or for one of its constituent parts.
Given the guidance aim of this document, it does not contain detailed procedures for performing the validation
tasks (such as number of laboratories, number of samples, etc.).
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2 Validation of reference methods

2.1 General
In this document reference methods are test methods that have been validated and of which the quality of the
test method is, given a specific field of application, accepted by experts and users. It might
...