Quantification of selected analgesics and their metabolites in influent wastewater by liquid chromatography tandem mass spectrometry.

Wastewater-based epidemiology (WBE) is an established tool to analyse patterns of community drug use. In recent times, monitoring the use of analgesics has become a public health priority. An analytical method was developed, optimised and validated for a broad range of common analgesics (non-steroidal anti-inflammatories and opioids) and their metabolites at trace concentrations in wastewater influent. Samples were analysed via liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) with an electrospray ionization source (ESI) in both positive and negative ion multiple reaction monitoring modes. Fifteen of the thirty-five biomarkers were validated for LC-MS/MS analysis by direct injection, while the other 20 biomarkers were present in wastewater at lower concentrations, requiring extraction by solid phase extraction (SPE) using Oasis HLB cartridges. The limit of quantification (LOQ) ranged between 17 ng/L - 191 ng/L and 13 ng/L -110 ng/L for direct injection and SPE, respectively. Recoveries for SPE ranged between 80% and 120%. Following validation, the method was applied to 28 wastewater samples from four municipal wastewater treatment plants. Twenty-eight of the thirty-five analgesic biomarkers were detected in the samples at concentrations of between 0.03 and 289 μg/L. Population normalised mass loads ranged from 10 mg/day/1000 (meperidine) to 72,000 mg/day/1000 (paracetamol) among all investigated compounds. The described method is a suitable analytical tool for wastewater-based epidemiology applications to estimate analgesics consumption.