Multi-residue analysis of selected pharmaceuticals in wastewater samples by stir-bar sorptive extraction followed by liquid desorption and liquid chromatography-mass spectrometry

New organic pollutants such as pharmaceuticals have been recently classified as emerging pollutants. These are chemically active compounds and may pose a risk to environmental organisms as well as to humans. Nowadays, separation and analytical techniques enable detection and quantification at extremely low concentrations. We aimed to develop and optimise a new method that would minimise (organic) solvent consumption and miniaturise and simplify sample preparation through the use of stirbar sorptive extraction of selected pharmaceuticals, followed by liquid desorption and liquid chromatography coupled to mass spectrometry. Several conditions and parameters that affect the extraction procedure (extraction time, sample pH, sample volume, extraction temperature, and addition of salt and organic modifier) were evaluated for suitable extraction efficiency. The optimised method (sample volume, 20 mL; sample pH, 9; extraction time, 150 min; and desorption time, 15 min; in an acetonitrile and methanol [50 : 50 v/v] mixture at 50 degrees C, without any added modifier) was validated and provided recoveries above 80% for 12 analytes, and for 6 analytes they were between 45% and 65%, while for another 6 analytes the recoveries were below 25%. The method provided a wide linear range (mainly 1.25-1250 ng L-1, R-2 > 0.99) with very low limits of quantification for all analytes (1.25-5.0 ng L-1). The method was used to test 15 wastewater samples and 22 out of 24 monitored pharmaceuticals were detected, generally in concentrations below 200 ng L-1.