Determination of acidic drugs and caffeine in municipal wastewaters and receiving waters by gas chromatography–ion trap tandem mass spectrometry

Some aspects of both sample preparation and instrumental techniques for analysis of such acidic drugs as acetylsalicylic acid, ibuprofen, gemfibrozil, fenoprofen, naproxen, ketoprofen, and diclofenac, as well as caffeine in surface water and municipal wastewater have been studied and further developed. Water samples were filtered and target analytes were extracted by solid-phase extraction (SPE). Supelco LC-18 and Oasis HLB SPE cartridges were used to pre-concentrate samples for acidic drugs and caffeine, respectively. A methylation process was applied to acidic drugs prior to analysis while caffeine was analyzed directly. A method of gas chromatography–ion trap tandem mass spectrometry (IT–MS/MS) for analysis of the target acidic pharmaceuticals and caffeine is presented here in detail. Such parameters as collision-induced dissociation (CID) voltage, isolation time, excitation time, excitation storage level, and electron energy were adjusted in order to optimize the instrument analytical performance. After optimization, an instrument detection limit of 0.5–20 pg/μL with signal-to-noise (S/N) not less than 5 was achieved for all target analytes. It was shown that this method has good linearity within the range of 10–2000 pg/μL. The application of the optimized IT–MS/MS parameters conjointly with the sample preparation procedure resulted in method detection limits (MDLs) of 0.1–1.0 and 20 ng/L for the determination of acidic drugs and caffeine, respectively in such samples as surface water, effluent from municipal wastewater plants, as well as receiving waters.