Simultaneous analysis of multi-class antibiotics in bottled water using large-volume direct-injection LC-MS/MS

A large-volume direct-injection (LVDI) method was developed and validated for the simultaneous analysis of 69 antibiotics in bottled water using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Target antibiotics included 23 sulfonamides, 19 quinolones, 12 macrolides, 11 β-lactams, and 4 tetracyclines. Optimization of ion source parameters led to enhanced signal intensities for 55 antibiotics. The 100 μL injection volume was both feasible and preferred, resulting in increased signal intensities while maintaining unchanged peak shapes for the antibiotics. Good absolute recoveries for the 69 antibiotics were obtained with the LVDI method, primarily ranging from 80% to 120%, whereas lower absolute recoveries of macrolides, quinolones, sulfonamides and β-lactams were observed with a solid-phase extraction (SPE) method. The limits of detection (LODs) for antibiotics were generally comparable between the LVDI and SPE methods, with values below 1 ng L^-1 for most antibiotics (0.00271-26.6 ng L^-1). Analysis of 25 brands of bottled water using the LVDI method revealed the presence of 54 antibiotics from 5 classes, with detection frequencies (DFs) ranging from 4% to 100% and detected concentrations between 0.0453 and 37.4 ng L^-1. Multiple antibiotics were detected simultaneously in bottled water, with more than 10 antibiotics identified in each of 9 different brands. Quinolones and sulfonamides were the predominant antibiotics, accounting for over 80% of the total concentration. Only sulfaclozine showed significantly different concentrations between purified drinking water and natural mineral water (22.2 vs. 17.2 ng L^-1, p < 0.05).