Quality Assurance in the Analytical Chemistry Laboratory
D Brynn Hibbert
Published:
2007
Online ISBN:
9780197562093
Print ISBN:
9780195162127
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Quality Assurance in the Analytical Chemistry Laboratory
D Brynn Hibbert
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D Brynn Hibbert
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203–226
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Published:
March 2007
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Hibbert, D Brynn, 'Metrological Traceability', Quality Assurance in the Analytical Chemistry Laboratory (
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Abstract
The ability to trace a measurement result to a reference value lies at the heart of any measurement. Traceability is part of standards governing laboratory practice, such as ISO/IEC 17025 and Good Laboratory Practice (see chapter 9), as a mandatory property of a measurement result, yet as a concept, traceability of a chemical measurement result is poorly understood. It is either taken for granted, often without much foundation, or ignored altogether. Why is traceability so important? How have we been able to ignore it for so long? The International Union of Pure and Applied Chemistry (IUPAC) has applied itself to this problem and a definitive discussion on metrological traceability in chemistry will be published. In this chapter I use the term “metrological traceability” to refer to the property of a measurement result that relates the result to a metrological reference. The word “metrological” is used to distinguish the concept from other kinds of traceability, such as the paper trail of documentation, or the physical trail of the chain of custody of a forensic sample. When the term “traceable standard” is used to refer to a calibration material, for example, the provenance of the material is not at issue, but the quantity value embodied in the standard. In explaining the importance of metrological traceability, I return to the discussions about chemical measurement (chapter 1). The concentration of a chemical is never measured for its own sake, but for a purpose, which often involves trade, health, environmental, or legal matters. The ultimate goal is achieved by comparing the measurement result with another measurement result, with a prescribed value, a legal or regulatory limit, or with values amassed from the experience of the analyst or client. In trading grain, for example, if exported wheat is analyzed by both buyer and seller for protein content, they should be confident that they will obtain comparable measurement results; in other words, results for the same sample of wheat should agree within the stated measurement uncertainties. If the results do not agree, then one party or the other will be disadvantaged, the samples will have to be remeasured, perhaps by a third-party referee, at cost of time and money.
Keywords: analyte, blood, calibrator, influence factor, matrix, national metrology institutes, precision, quantity, recovery, sampling
Subject
Analytical Chemistry
Collection: Oxford Scholarship Online
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