Optimization and application of a sensitive UPLC-MS/MS method for the quantitative determination of antibiotics in PM_2.5

The increasing occurrence of antibiotics in the environment has raised concerns about their atmospheric transport, human exposure, and potential contribution to antibiotic resistance dissemination. In this study, a sensitive ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for the simultaneous determination of 74 antibiotics from multiple classes in fine particulate matter (PM_2.5). Key chromatographic and sample-preparation parameters were systematically optimized. Optimal performance was achieved using a T3 chromatographic column, mobile phases containing 0.1% (v/v) formic acid, Oasis HLB cartridges for solid-phase extraction, 0.1 mol/L disodium ethylenediaminetetraacetate, and methanol containing 1% (v/v) formic acid as the elution solvent. These conditions improved extraction efficiency, chromatographic performance, and quantitative sensitivity while reducing matrix-related interference. The validated method yielded accuracy values of 69.7%-131.7% and relative standard deviations of 1.0%-18.1% at three fortification levels, with estimated method quantification limits as low as 0.37 pg/m³. The method was applied to 29 ambient PM_2.5 samples collected over 24-h periods in Beijing. Twenty-two antibiotics were detected above their respective method detection limits, with concentrations reaching 121.38 pg/m³. Seven compounds exhibited detection frequencies above 50%, and roxithromycin was detected in all samples. Oxytetracycline showed the highest mean concentration among the quantifiable results, at 14.48 pg/m³. Compared with previously reported methods that generally cover fewer antibiotic classes or focus on conventional environmental matrices, the proposed method enables sensitive and simultaneous determination of a broad range of antibiotics in the analytically challenging PM_2.5 matrix. It therefore provides a comprehensive workflow for monitoring airborne antibiotics and supporting subsequent exposure and environmental-occurrence studies.