International interlaboratory study of forensic ethanol standards

Abstract

In March, 1996, CITAC (Cooperation on International Traceability in Analytical Chemistry) initiated a task to assess the comparability of the standards used in different countries. The Laboratory of the Government Chemist (LGC) acted as the project leader. Three certified solutions with nominal ethanol concentrations in water of 50, 80 and 200 mg per 100 ml were distributed to sixteen standards laboratories in Europe, Asia, North America and Australia. The laboratories analysed the solutions by methods of their choice and reported the results, together with measurement uncertainty data and other information such as accreditation status and level of experience. Six out of sixteen laboratories fully met the study target criteria of the mean results for all three solutions being within ±1% of the certified values. Participants were encouraged to assess the adequacy of their performance for their particular application. The paper reports the study protocol, the results of the interlaboratory comparison and discusses the results in the context of the metrological performance required to support routine measurement used for prosecution purposes.