1.2 Specificity of Chemical Metrology
7
content of a given substance (analyte) in the sample, apart from the need to use
the calibrated instrument properly, it is also necessary to establish the influence of
the accompanying sample components (the chemical matrix) on the final result. In
chemical analyses, the validation of the whole analytical procedure is crucial, and
should include sampling, sample preparation, measurement of the given properties,
and evaluation of the influence of the matrix on the measurement’s result and the
evaluation of the influence of all of these parameters on the final test result.
A great deal of discussions and controversies are evoked by the use of the terms
‘measurement’ and ‘test.’ They are not synonymous; their meanings differ and their
concepts are described in the following documents, respectively: ISO/IEC Guide 99
(VIM) and EA-04/16. The distinction in the meaning of those terms and their correct
use is important.
Measurement: the process of experimentally obtaining one or more quantity values
that can reasonably be attributed to a quantity. [Clause 2.1; ISO/IEC Guide 99 (VIM)]
Test: technical operation that consists of the determination of one or more characteristics of a given product, process or service according to a specified procedure.
[Chapter 5.2; EA—4/16 G:2003 EA guidelines on the expression of uncertainty in
quantitative testing]
Following the more detailed description given in EA-4/16 G:2003, it is clear that in
general a measurement process yields a result that is independent of the measurement
method, while the only difference relates to uncertainty associated with a particular
method. In the example of the temperature measurements of a given object, apart from
the type of thermometer, the measured values should be the same, varying only with
the uncertainty that depends on the performance of the thermometer. By contrast,
a test result depends on the method of measurement and on the specific procedure
used to determine the given property. As a consequence, different test methods may
yield different results. Thus, in the case of measurement procedures, environmental
and operational conditions will either be maintained at standardized values or be
measured in order to apply correction factors and to express the result in terms of
standardized conditions. From the given description it follows that measurement is
an integral part of a test.
Accordingly, the responsibility of a chemical testing laboratory is not limited to
performing a measurement of the agreed chemical properties of the object delivered
by the client but also includes the entire analytical procedure established to be fit for
the purpose of the client’s need. This requires the designing of a proper technical
procedure that is adequate for the objective, for which the measurement results will
be used.
It is worth emphasizing here that this book is addressed to those who mostly
deal with the measurement of chemical properties. Hence in the following chapters,
particular attention will be paid to the metrological aspects of the analytical procedure
executed by the chemical laboratory (excluding sampling from the entire object),
namely: laboratory sample preparation, measurement, and estimation of the influence
of matrix components and the conditions of sample preparation on the measurement
result. Of course, aspects related to the calibration of measuring instruments will also
be considered. Nevertheless, a lot of attention will be focused on the fact that the result
7
content of a given substance (analyte) in the sample, apart from the need to use
the calibrated instrument properly, it is also necessary to establish the influence of
the accompanying sample components (the chemical matrix) on the final result. In
chemical analyses, the validation of the whole analytical procedure is crucial, and
should include sampling, sample preparation, measurement of the given properties,
and evaluation of the influence of the matrix on the measurement’s result and the
evaluation of the influence of all of these parameters on the final test result.
A great deal of discussions and controversies are evoked by the use of the terms
‘measurement’ and ‘test.’ They are not synonymous; their meanings differ and their
concepts are described in the following documents, respectively: ISO/IEC Guide 99
(VIM) and EA-04/16. The distinction in the meaning of those terms and their correct
use is important.
Measurement: the process of experimentally obtaining one or more quantity values
that can reasonably be attributed to a quantity. [Clause 2.1; ISO/IEC Guide 99 (VIM)]
Test: technical operation that consists of the determination of one or more characteristics of a given product, process or service according to a specified procedure.
[Chapter 5.2; EA—4/16 G:2003 EA guidelines on the expression of uncertainty in
quantitative testing]
Following the more detailed description given in EA-4/16 G:2003, it is clear that in
general a measurement process yields a result that is independent of the measurement
method, while the only difference relates to uncertainty associated with a particular
method. In the example of the temperature measurements of a given object, apart from
the type of thermometer, the measured values should be the same, varying only with
the uncertainty that depends on the performance of the thermometer. By contrast,
a test result depends on the method of measurement and on the specific procedure
used to determine the given property. As a consequence, different test methods may
yield different results. Thus, in the case of measurement procedures, environmental
and operational conditions will either be maintained at standardized values or be
measured in order to apply correction factors and to express the result in terms of
standardized conditions. From the given description it follows that measurement is
an integral part of a test.
Accordingly, the responsibility of a chemical testing laboratory is not limited to
performing a measurement of the agreed chemical properties of the object delivered
by the client but also includes the entire analytical procedure established to be fit for
the purpose of the client’s need. This requires the designing of a proper technical
procedure that is adequate for the objective, for which the measurement results will
be used.
It is worth emphasizing here that this book is addressed to those who mostly
deal with the measurement of chemical properties. Hence in the following chapters,
particular attention will be paid to the metrological aspects of the analytical procedure
executed by the chemical laboratory (excluding sampling from the entire object),
namely: laboratory sample preparation, measurement, and estimation of the influence
of matrix components and the conditions of sample preparation on the measurement
result. Of course, aspects related to the calibration of measuring instruments will also
be considered. Nevertheless, a lot of attention will be focused on the fact that the result