Quantitative analysis of antibiotics in aquifer sediments by liquid chromatography coupled to high resolution mass spectrometry

• Twenty-five antibiotics from aquifer sediments are successfully extracted by MASE.
• Quantitative analysed in Target-SIM-dd-MS2 scan mode with LC-Q-Orbitrap.
• Antibiotics were observed in 4.0, 7.5, 13.0 and 18.0 m depth of sediments in aquifer.

A highly effective analytical method for multi-residue determination of antibiotics in aquifer sediments was first established in this study. Microwave-assisted solvent extraction (MASE) and solid-phase extraction were used for sample pre-concentration and purification, ultra-high performance liquid chromatography coupled to hybrid quadrupole—high resolution Orbitrap mass spectrometry (UHPLC-Q-Orbitrap) was applied for detection. For high resolution mass spectrometry (HRMS), the target compounds were tentatively identified by retention time and accurate mass which was measured with precursor ions in Target-SIM scan, and then confirmed by the monitoring of daughter ion fragments which were generated in dd-MS2 scan. The results provided good mass accuracy with mass deviations below 2 ppm (except norfloxacin with −2.3 ppm) for quantitative analysis of the compounds by HRMS. Reasonable recoveries of all analytes were obtained more than 60% (except doxytetracycline) in fortification samples at concentrations higher than 10 μg kg−1. Relative standard deviations of repeatability and inter-day precision were below 21% and 11%. Limits of detection (LOD) ranged from 0.1 to 3.8 μg kg−1, whereas limits of quantification (LOQ) were established between 0.3–9.0 μg kg−1. The method was applied to analyze real aquifer sediment samples in different aquifer depth of 4.0, 7.5, 13.0 and 18.0 m. Chlorotetracycline and ofloxacin were observed at relative high concentrations of 53 and 19 μg kg−1 respectively in 18.0 m deepness. The exposure to low doses of these compounds in subsurface environment increases concerns on long-term ecological security of underground system.