130
3 Traceability: Reference Materials
Example: CRMs, IRMs, previously analysed samples.
External evaluation. This is entrusted to personnel belonging to neither the laboratory nor
its parent body. There are two possible alternatives:
(a) Use of a CRM supplied by an external institution proficient in laboratory accreditation
processes.
(b) Use of a CRM or IRM for mUltiple analyses by va rious laboratories, as in inter-laboratory
studies aimed at testing the proficiency of the participants by comparison with one
another (and with the certified value if the sample is a CRM).
3.6 Specific Meanings of Traceability
Although, metrologically, traceability is almost invariably used to refer to a property of a result, there is no plausible reason to exclude application to other
analytical entities. In the following sections, the traceability concept is extended
to various analytical concepts in accordance with ISO's recommendations in
defining traceability in relation to quality management and quality assurance.
I 3.6.1 Traceability of an Analytical Result
In 1993, ISO defined traceability as a "property of the result of a measurement or
the value of a standard whereby it can be related to stated references, usually
national or international standards, through an unbroken chain of comparisons
all having stated uncertainties". The boldfaced phrases in this definition are
additions introduced after the original ISO definition of 1984 was issued, additions that extend application to standards - as done in this chapter - and
underscore the significance of the uncertainty arising in the comparisons, which
must unavoidably accompany every analytical result, whether partial or global.
The official definition of traceability of a result only considers one of its
aspects (viz. its relationship to standards). Although the other two, "history" and
"comparability" (Fig. 3.12), are implicitly included, they are highly relevant and
warrant some emphasis.
The "stated standards" in the definition are primary analytical standards that
should be related to chemical and base standards through the unbroken chain of
comparisons, where equipment and method calibration play crucial roles.
Reference materials (RMs) do not ensure traceability, so certified reference
materials (CRMs) must be used instead. If, for example, the response of an
atomic absorption spectrometer is calibrated with a commercially available
Pb(N03h solution, then an extrapolated result will have dubious traceability
since the comparison chain may have broken at some link. In fact, one should
ensure that the balance has been calibrated and that the instrument response has
been calibrated with a CRM (or an RM previously checked against a CRM). The
result of a CMP will have the stated traceability provided the process has been
applied to a certified sample standard (a CRM).
3 Traceability: Reference Materials
Example: CRMs, IRMs, previously analysed samples.
External evaluation. This is entrusted to personnel belonging to neither the laboratory nor
its parent body. There are two possible alternatives:
(a) Use of a CRM supplied by an external institution proficient in laboratory accreditation
processes.
(b) Use of a CRM or IRM for mUltiple analyses by va rious laboratories, as in inter-laboratory
studies aimed at testing the proficiency of the participants by comparison with one
another (and with the certified value if the sample is a CRM).
3.6 Specific Meanings of Traceability
Although, metrologically, traceability is almost invariably used to refer to a property of a result, there is no plausible reason to exclude application to other
analytical entities. In the following sections, the traceability concept is extended
to various analytical concepts in accordance with ISO's recommendations in
defining traceability in relation to quality management and quality assurance.
I 3.6.1 Traceability of an Analytical Result
In 1993, ISO defined traceability as a "property of the result of a measurement or
the value of a standard whereby it can be related to stated references, usually
national or international standards, through an unbroken chain of comparisons
all having stated uncertainties". The boldfaced phrases in this definition are
additions introduced after the original ISO definition of 1984 was issued, additions that extend application to standards - as done in this chapter - and
underscore the significance of the uncertainty arising in the comparisons, which
must unavoidably accompany every analytical result, whether partial or global.
The official definition of traceability of a result only considers one of its
aspects (viz. its relationship to standards). Although the other two, "history" and
"comparability" (Fig. 3.12), are implicitly included, they are highly relevant and
warrant some emphasis.
The "stated standards" in the definition are primary analytical standards that
should be related to chemical and base standards through the unbroken chain of
comparisons, where equipment and method calibration play crucial roles.
Reference materials (RMs) do not ensure traceability, so certified reference
materials (CRMs) must be used instead. If, for example, the response of an
atomic absorption spectrometer is calibrated with a commercially available
Pb(N03h solution, then an extrapolated result will have dubious traceability
since the comparison chain may have broken at some link. In fact, one should
ensure that the balance has been calibrated and that the instrument response has
been calibrated with a CRM (or an RM previously checked against a CRM). The
result of a CMP will have the stated traceability provided the process has been
applied to a certified sample standard (a CRM).