Multi-year interlaboratory exercises for the analysis of illicit drugs and metabolites in wastewater: development of a quality control system

Abstract

This study presents the development of a worldwide inter-laboratory testing scheme for the analysis of seven illicit drug residues in different matrices (standard solutions, tap- and wastewater). By repeating this exercise for six years with participation of 37 laboratories from 25 countries, the testing scheme was substantially improved based on experiences gained across the years (e.g. matrix type, sample conditions, spiking levels). From the exercises, (pre-)analytical issues (e.g. pH adjustment, filtration) were revealed for some analytes which resulted in formulation of best-practice protocols, both for inter-laboratory setup and analytical procedures. The results illustrate the effectiveness of the inter-laboratory testing scheme in assessing laboratory performance in the framework of illicit drug analysis in wastewater. The exercise proved that measurements of laboratories were of high quality (> 80% satisfactory results for 6 out of 7 analytes) and that analytical follow-up is important to assist laboratories in improving robustness of wastewater-based epidemiology results.