Selective determination of COXIBs in environmental water samples by mixed-mode solid phase extraction and liquid chromatography quadrupole time-of-flight mass spectrometry

• An efficient procedure for the sample preparation of water (superficial and wastewater) samples for the determination of several COXIBs has been developed.
• The use of mixed-mode SPE for sample preparation reduce matrix effects to vary low limits, thus making easy the calibration and determination.
• Using exact mass (LC-QTOF) liquid chromatography–mass spectrometry allows unambiguous detection and determination of analytes and also metabolites using a post-target approach.

The development and performance evaluation of a method for the simultaneous determination of six pharmaceuticals belonging to the class of non-steroidal anti-inflammatory drugs (NSAIDs) which present high selectivity for the cyclooxygenase (COX)-2 isoform of COX (COXIBs) in environmental waters are presented. The method involves an off-line mixed mode (reversed-phase and strong anionic exchange) solid phase extraction (SPE) for the selective concentration of COXIBs in combination with liquid chromatography (LC) quadrupole time-of-flight (QTOF) mass spectrometry (MS). The use of a strong anionic exchange sorbent (Oasis MAX) led to a significant reduction of matrix effects, during electrospray ionization (ESI), in comparison with results obtained for mixed mode weak anionic exchange sorbent (Oasis Wax) and polymeric reversed phase sorbents (Oasis HLB and Strata X).The developed method attained limits of quantification (LOQs) between 0.01 and 0.20 ng L−1 for river water and effluent wastewater and, for influent wastewater this limits were ranged between 0.03 and 0.45 ng L−1.Among the pharmaceuticals investigated, two of them (celecoxib and etoricoxib) were detected at low levels (ppt) in real samples of treated and raw wastewaters, and two metabolites were also found; the carboxylated celecoxib and the hydroxylated etoricoxib.