Optimizer

The targets, AZI, ERY, and ROX, in the WWTP influents and effluents were analyzed by high-performance liquid chromatography interfaced with tandem mass spectrometry (HPLC-MS/MS, Agilent 6410 triple quadrupole MS) that was equipped with an electrospray ionization (ESI) source in multiple reaction monitoring (MRM) mode. All three target antibiotics were analyzed in positive MRM mode. A 10-μL aliquot of extract was injected onto an Agilent Eclipse XDB-C18 (3.0 × 75 mm, 3.5 μm) column with a poroshell 120 precolumn filter (3.0 mm, 0.2 μm). The column temperature was kept at 40 °C for the analysis. The mobile phases 0.1% (v/v) formic acid (A) and acetonitrile (B) were used, under the following gradient conditions: 0 min, 5% B; 5 min, 40% B; 8 min, 80% B; 16 min, 95% B, and 19 min, 5% B. The flow rates of the mobile phases were 0.3 mL/min, and the mass spectrometry conditions were optimized using Optimizer (Agilent, USA) for the fine tuning of the fragmentor voltage, collision energy (CE) and MRM transitions for the AZI, ERY, and ROX. Nitrogen gas was used as the drying and collision gas. The following optimized parameters were selected: drying gas temperature 200 °C, drying gas flow rate 6 mL/min, and capillary voltage 4200 V. The system was re-equilibrated for 10 min between runs.