Dilute-and-shoot approach for the high-throughput LC-MS/MS determination of illicit drugs in the field of wastewater-based epidemiology.

The determination of illicit drugs in urban influent wastewater (IWW) enables the monitoring of spatial and temporal drug usage trends and assessment of community lifestyle habits. The increasing number of wastewater surveillance studies has emphasized the necessity for the development of rapid, high-throughput methods that maintain high quality data. This work evaluates the use of a dilute-and-shoot methodology, based on direct injection (DI) of centrifuged samples, as an alternative approach to the widely applied sample pre-treatment based on solid-phase extraction, for the liquid chromatography-tandem mass spectrometry determination of seven widely consumed illicit drugs and their metabolites in IWW (amphetamine; cocaine metabolite, benzoylecgonine; ketamine; 3,4-methylenedioxymethamphetamine (MDMA); methamphetamine; cannabis metabolite, 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THCCOOH); heroin metabolite, 6-acetylmorphine (6-MAM)). Comparison of both approaches in terms of matrix effects, sensitivity and accuracy, demonstrates the DI method suitability to correctly quantify these analytes in IWW, with a limit of quantification lower than 30 ng L for most compounds. After validation of the method and participation in an interlaboratory exercise, the DI method was applied to the analysis of 54 IWW samples collected from different Spanish wastewater treatment plants. Additionally, quality controls were incorporated in each analysis batch to support the DI method applicability and robustness. The use of a 10 μL-DI reduces time-consuming sample preparation, analysis time and measurement uncertainty. Moreover, it supports green chemistry by reducing the consumption of organic solvents and it facilitates logistics by collecting, transporting, and storing less sample volume. The methodology is therefore especially appropriate for monitoring illicit drugs in large wastewater-based epidemiology sampling campaigns or when fast near real-time results are needed.