Liquid chromatography-tandem mass spectrometry to determine sedative hypnotic drugs in river water and wastewater

A method for simultaneous determination of four benzodiazepines (bromazepam (BMZ), carbamazepine (CBZ), diazepam (DZP) and nordiazepam (NDZ)) and four barbiturates (barbital (BTL), pentobarbital (PTB), phenobarbital (PNB) and secobarbital (SCB)) in river water and wastewater using solid-phase extraction (SPE) followed by liquid chromatography-(electrospray) tandem mass spectrometry (LC-(ESI)MS/MS) was developed. LC-(ESI)MS/MS analysis was performed in positive and negative modes for benzodiazepines and barbiturates, respectively, and in selected reaction monitoring (SRM). Limits of detection (LODs) were in the range of 0.2–5 ng/L for benzodiazepines and 2.5–50 ng/L for barbiturates. Precision (repeatability and reproducibility between days) expressed as %RSD (n = 5) was lower than 17% for low concentration (depending on the matrix between 50 and 250 ng/L for barbiturates, and between 5 and 25 ng/L for benzodiazepines), and lower than 15% for high concentration (between 200 and 1250 ng/L for barbiturates, and between 20 and 125 ng/L for benzodiazepines). Low matrix effect was observed for all compounds, except for BTL (75%) and PTB (–48%) in wastewater. The method was applied to water samples from two sewage treatment plants (STPs) and the rivers Ebre, Ter and Llobregat, located in Catalonia. CBZ was the target compound found at the highest concentration in river water (2.1–3.3 ng/L). In both influent and effluent wastewater samples, PNB, BMZ, CBZ, DZP and NDZ were determined at concentration levels ranging from 5.0 to 2337.3 ng/L.