Determination of illicit drugs in seized materials: role of sampling and analysis in estimation of measurement uncertainty

The determination of illicit active ingredients in seized materials, in order to assess penal or administrative offences, is routinely carried out in many forensic toxicology laboratories. This paper presents main features of the protocol adopted in the Authors' laboratory for the above investigations. In particular, sampling and analysis are considered as the same measurement process quantifying their combined contribution to overall measurement uncertainty. Aspects concerning representative sampling in the case of single and multiple items are discussed. The effects of material heterogeneity are considered by analyzing separately distinct primary samples taken from different parts of the sampling target. Possible errors due to particles dimension that could arise when sub-sampling are also considered. Analytical precision, bias and other matrix effects are studied in order to quantify the component of the overall measurement uncertainty associated to the analysis of prepared test samples. Typical scenarios arising when measurement results are used to assess compliance with specification limits are also discussed revealing the crucial role of measurement uncertainty.