The development and application of a system for simultaneously determining anti-infectives and nasal decongestants using on-line solid-phase extraction and liquid chromatography–tandem mass spectrometry

A method for the simultaneous analysis of antibiotics, antiviral and nasal decongestants in treated sewage effluent and surface water has been developed and validated. The method uses on-line solid phase extraction (SPE) of injected high-volume samples in conjunction with liquid chromatography–tandem mass spectrometry (LC–MS/MS). This method includes a range of antibiotics (Trimethoprim, Oxytetracycline, Ofloxacin, Norfloxacin, Ciprofloxacin, Azithromycin, Doxycycline, Sulfamethoxazole, Erythromycin and Clarithromycin), an antiviral (Oseltamivir) and nasal decongestants (Naphazoline, Oxymetazoline and Xylometazoline). The method's detection limits (MDLs) ranged from (0.2 ng L−1) to (3.1 ng L−1), based on a 1 mL extraction volume. Its intra-day precision was determined by performing nine runs with 200 ng L−1 samples; the intra-day relative standard deviation (RSD) ranged from 1% to 19%. Inter-day precision was determined by analyzing samples in triplicate over the course of three days, yielding relative standard deviations ranging from <5% to <26%. The linearity (R2) for all compounds tested was >0.90. Spike relative recoveries ranged from 40% to 157% and 40% to 152% for STP effluent and surface water samples, respectively. Finally, the method was used to analyze real effluent and surface water.