Optimization and validation of a hydrophilic interaction liquid chromatography-tandem mass spectrometry method for the determination of 13 top-prescribed pharmaceuticals in influent wastewater

A sensitive hydrophilic interaction liquid chromatography (HILIC)-tandem mass spectrometry method was developed and validated for the analysis of 13 pharmaceuticals (omeprazole, pantoprazole, ranitidine, citalopram, fluoxetine, paroxetine, venlafaxine, tramadol, nebivolol, metoprolol, atenolol, bisoprolol and metformin) in influent wastewater. The analytes were selected from the list of top-sold prescription pharmaceuticals in Belgium. The HILIC separation was optimised to achieve quantification of all analytes in real influent wastewater samples where other compounds, mainly metabolites of some of the pharmaceuticals, were found to interfere even with mass-spectrometric detection in multiple reaction monitoring (MRM) mode. Sample cleanup and preconcentration was based on solid-phase extraction, and Oasis HLB cartridges were chosen after optimization. The method was validated by assessing the following parameters: specificity, selectivity, lower limit of quantification (LLOQ), linearity, accuracy, precision, recovery and matrix effects. For each analyte, LLOQs were sufficiently low to provide a good analytical performance at concentrations expected in real influent samples. Typical LLOQs were 1 ng/L, except for metformin (500 ng/L). Six deuterated analogues were used as internal standards. A total of 22 influent wastewater samples collected from 18 different wastewater treatment plants in Belgium were analysed. Most analytes were present in the samples at concentrations above the LLOQ and were in agreement with other results from the literature. Nebivolol was for the first time found in influent wastewater. In the future, this analytical method will be used to determine if there is a relationship between pharmaceutical sales figures and concentrations of these compounds in influent wastewater.