[Optimization and Validation of the Analytical Method to Detect New Psychoactive Substances in Wastewater]

New psychoactive substances (NPS) are emerging continuously, as the crackdown against traditional drugs becomes stricter. Metabolites of NPSs and the unchanged drugs enter wastewater through urine and are collected and treated by wastewater treatment plants before being discharged into the aquatic environment. Based on previous research, solid phase extraction (SPE) and ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) were used and the detection method of 11 NPSs was optimized. Influences of wastewater pretreatment procedures, including SPE columns; pH values of water samples; and processes of flushing and redissolving on NPS recoveries were compared. It was shown that the best recovery was achieved when Oasis MCX columns were used and the pH value of wastewater samples was adjusted to 2. A flushing process with 2 mL water at pH=2 followed by 2 mL methanol was needed. Redissolution of the residue after evaporation was best achieved with 400 μL of a 20% methanol water solution. It was indicated by retention times, recoveries, matrix effects, limits of detection, limits of quantification, as well as precision that C18-UPLC-MS/MS and the optimized method are efficient and valid. Influent and effluent samples from 11 municipal wastewater treatment plants in Beijing were analyzed using the optimized method for validation. The validated method can be used as an important reference for monitoring NPSs via wastewater-based epidemiology and for assessing the risk of NPS abuse in China.