Open-access Measurement Uncertainty Calculator MUCalc and its application to the quantification of Etizolam in tablets using High-Performance Liquid Chromatography (HPLC)

Abstract

The assessment of measurement uncertainty of an analytic method is a requirement for forensic toxicologists and drug chemists. There are two main methods for estimating measurement uncertainty: the bottom-up and the top-down approaches. The bottom-up approach has been suggested in current practice guides including ‘Guide to the Expression of Uncertainty in Measurement (GUM)’ published by ISO, and a guide to ‘Quantifying Uncertainty in Analytical Measurement’ published by EURACHEM. To support forensic practitioners needing to estimate measurement uncertainty, we have developed an open-access Measurement Uncertainty Calculator (MUCalc) based on a bottom-up approach. The software quantifies measurement uncertainty associated with sample homogeneity, method precision, calibration curve, calibration standard and sample preparation. These are then combined to estimate the combined and the expanded uncertainty. The calculations are carried out in accordance with standards set out by accreditation organisations such as ISO/IEC Guid 98, GUM, EURACHEM and UKAS. MUCalc is unique in the sense that it is a white box. It displays on screen all formulae and step-by-step guide calculations in an easy-to-follow approach. This makes it easy for users to understand and cross-examine every result generated by MUCalc. Such a transparent display of the workings of the calculation is essential for the purposes of disclosure within the legal domain. It also facilitates training in the calculation of measurement uncertainties. We demonstrate the use of MUCalc for estimating the uncertainty associated with the quantification of the concentration of etizolam, a benzodiazepine implicated in a large percentage of drug-related deaths in Scotland.