Fast UHPLC-MS/MS for the Simultaneous Determination of Azithromycin, Erythromycin, Fluoxetine and Sotalol in Surface Water Samples

Chromatographic development for the determination of pharmaceuticals in environmental water samples is particularly challenging when the analytes have significantly different physico-chemical properties (solubility, polarity, pKa) often requiring multiple chromatographic methods for each active component. This paper presents a method for the simultaneous determination of azithromycin, erythromycin (antibiotics), fluoxetine (anti-depressant) and sotalol (b-blocker) in surface waters by ultra-high-performance liquid chromatography coupled with ultra-high-resolution time-of-flight mass spectrometry. These pharmaceuticals—presenting a broad spectrum of polarity (0.24 ≤ log Kow ≤ 4.05)—were separated on a C-18 analytical column, after a simple filtration step for freshwater samples or after a liquid–liquid extraction with Methyl-tertio-butyl ether (MTBE) for seawater samples. The optimized separation method (in terms of nature of column and eluent, elution gradient, and of mass spectrometric parameters), enable one to reach limits of detection ranging between 2 and 7 ng L−1 and limits of quantification between 7 and 23 ng L−1 for the four targeted molecules, within a three minute run. This method was validated using samples collected from three different surface waters in Lebanon (freshwater and seawater) and analytical results were compared with those obtained in surface waters sampled in a French river, equivalent in terms of human activities. Using this method, we report the highest concentration of pharmaceuticals found in surface water (up to 377 ng L−1 and 268 ng L−1, respectively, for azithromycin and erythromycin, in the Litani river, Lebanon).