Determination of antibiotics in Brazilian surface waters using liquid chromatography-electrospray tandem mass...

A liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS) method for the determination of antibiotics in water was developed and applied to Brazilian surface waters. Amoxicillin, ampicillin, cefalexin (CEF), ciprofloxacin (CIP), norfloxacin (NOR), sulfamethoxazole, tetracycline (TET), and trimethoprim were selected as target compounds due to their high consumption pattern in Brazil. LC and MS conditions were optimized to produce the maximum analytic response for each compound. Anion exchange and polymeric solid-phase extraction cartridges, in series, were employed during the extraction procedures. Recovery, linear range, limit of detection (LOD), and limit of quantification were calculated. LOD varied from 0.13 ng L(-1) for CIP and NOR to 0.76 ng L(-1) for TET. Surface water samples from the Atibaia watershed (São Paulo State, Brazil) were analyzed. Results showed that seasonal and anthropogenic aspects dictated the levels of antibiotics in the samples. An overall frequency of detection of 55% was observed during the rainy period, whereas a higher percentage (88%) was noticed for samples collected during the dry season. In the Atibaia River, sample concentrations ranged from 29 ng L(-1) for CEF to 0.5 ng L(-1) for NOR. In a sewage-affected stream, however, concentrations up to 2422 ng L(-1) CEF were found.