Analysis of macrolide antibiotics in river water by solid-phase extraction and liquid chromatography-mass spectrometry.

A liquid chromatography-mass spectrometry (LC-MS) method was developed for the determination of five macrolides in natural water samples, using kitasamycin as surrogate. The macrolides were extracted from water samples using Oasis HLB cartridges. Pre-concentration factors up to 250 were obtained. Separation was carried out in an end-capped silica-based C18 column and mobile phases consisting of water/acetonitrile mixtures containing ammonium acetate. Detection was performed by mass spectrometry with a single quadrupole and a triple quadrupole using an electrospray interface. The quality parameters obtained with these two approaches were compared. The detection limits of the whole process were about 1 ng l(-1). The recoveries from 250 ml of water samples spiked at 25-125 ng l(-1) level were in the range 85-115%, except for azithromycin levels, which were around 70%. Erythromycin-H2O, clarithromycin and azithromyzin were found, at the sub ng l(-1) level, in the studied rivers.