Determination of 22 antibiotics in seawater by liquid chromatography-tandem mass spectrometry with large-volume injection

A new method was developed for the simultaneous determination of various trace antibiotics in seawater using solid-phase extraction (SPE) combined with large-volume injection liquid chromatography-tandem mass spectrometry (LVI-LC-MS/MS) and applied to the analysis of common antibiotics in nearshore bays. The optimization of offline SPE and online SPE (large volume injection) conditions was investigated. Under the optimal conditions, only 80 mL of seawater samples need to be enriched via an offline HLB SPE column, followed by detection through LVI-LC-MS/MS (injection volume of 50 μL). Remarkably, the low limit of detection (LOD) for the 22 targeted antibiotics falls within the range of 0.003～0.63 ng/L, while the limits of quantification (LOQ) are obtained in the range of 0.01～1.25 ng/L. Satisfactory recoveries (55.87%～113.49%), precision (relative standard deviations, 1.13%～12.60%), and linearity (R²>0.990) were also achieved, demonstrating the high sensitivity and precision of the proposed method. Moreover, compared to the conventional small-volume injection method, this method effectively improved sample utilization rate and significantly reduced both the required seawater sample volume and pretreatment time. Therefore, the method meets the requirements for the detection of trace antibiotics in the seawater environment. To test the effectiveness of the method, antibiotics were detected in seawater samples collected from two mariculture bays in Shandong, namely Sishili bay and Sanggou bay. A total of 9 common antibiotics were detected in 36 samples of surface and bottom seawater, mainly florfenicol, sulfamethoxazole, trimethoprim, clarithromycin, dehydrated erythromycin, and roxithromycin, with total average concentrations ranging from 0.05～8.19 ng/L.