4.5 Metrological Traceability in Practice
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to the peppermint leaves standard of known iron content. Perhaps some analysts
will argue this because they just saw peppermint leaves in the catalogue of RM, for
which a certified iron content was given. If so, they are in a very comfortable but,
unfortunately, rare situation.
However, before we content ourselves with buying the available RM on the market, we must ask a few questions regarding the similarity of the material and its
characteristics with the test sample, as well as the similarities of the procedure of
preparation of samples:
– Are peppermint leaves from plant derived from the same species (trees) as those
used by an RMP?
– Is the iron content similar to the content in the test samples?
– Does the reference value relate to the total iron content after complete digestion
of the sample or after extraction?
An RM, if it is as far as possible similar to the characteristics of the test sample,
may be an adequate source of metrological traceability, provided that the testing is
carried out in terms of recovery. These studies, in order to be a carrier of relevant
information, should be made according to the same measurement procedure that
was used for the samples. The recovery allows an assessment of the impact of the
measurement procedure on the final result. It is not important whether the recovery
is close to 100% or is more like 68%, as long as the value is repeatable within the
range of accepted accuracy and associated uncertainty.
4.6 Summary
Measurement traceability is an essential part of measurements because it allows
a result to be related to the recognized measurement standards. The measurement
procedures in chemistry are the most complex processes, thus ensuring traceability
cannot be considered to be a routine task and must include all elements of the process.
51
to the peppermint leaves standard of known iron content. Perhaps some analysts
will argue this because they just saw peppermint leaves in the catalogue of RM, for
which a certified iron content was given. If so, they are in a very comfortable but,
unfortunately, rare situation.
However, before we content ourselves with buying the available RM on the market, we must ask a few questions regarding the similarity of the material and its
characteristics with the test sample, as well as the similarities of the procedure of
preparation of samples:
– Are peppermint leaves from plant derived from the same species (trees) as those
used by an RMP?
– Is the iron content similar to the content in the test samples?
– Does the reference value relate to the total iron content after complete digestion
of the sample or after extraction?
An RM, if it is as far as possible similar to the characteristics of the test sample,
may be an adequate source of metrological traceability, provided that the testing is
carried out in terms of recovery. These studies, in order to be a carrier of relevant
information, should be made according to the same measurement procedure that
was used for the samples. The recovery allows an assessment of the impact of the
measurement procedure on the final result. It is not important whether the recovery
is close to 100% or is more like 68%, as long as the value is repeatable within the
range of accepted accuracy and associated uncertainty.
4.6 Summary
Measurement traceability is an essential part of measurements because it allows
a result to be related to the recognized measurement standards. The measurement
procedures in chemistry are the most complex processes, thus ensuring traceability
cannot be considered to be a routine task and must include all elements of the process.