Use of accumulated proficiency testing scheme results to evaluate laboratory performance in forensic ethanol analysis

In 2004, the National Metrology Institute of South Africa, NMISA (then the National Metrology Laboratory of the CSIR, South Africa) was requested by forensic testing laboratories to coordinate a proficiency testing scheme for the determination of ethanol in blood. This led to an annual proficiency testing scheme where the test materials used are aqueous ethanol certified reference materials prepared and certified by NMISA. This article describes the development of the scheme and the progress made by the regular participants in the scheme over twelve years. The ethanol concentrations of the test samples were between 0.01 g/ 100 g and 0.6 g/ 100 g. The measurement uncertainty and the expected method performance were conveniently estimated from the data collected over the years.