Optimization and Application of Pretreatment Process for the Enrichment of 20 Antibiotics in Water by Solid Phase Extraction

To establish a reliable and accurate solid-phase extraction (SPE) pretreatment method for multi-class antibiotics in water and achieve simultaneous determination of 20 antibiotics, including tetracyclines, quinolones, and sulfonamides, key pretreatment parameters were optimized via single-factor experiments in this study. The optimized parameters included pH of acidified water samples, Na2EDTA dosage, SPE cartridge type, operational conditions, and the type and volume of elution solvent. The validated method was further applied to analyze surface water samples collected from 16 sampling sites in Poyang Lake and its three typical tributaries (Ganjiang River, Jinjiang River, and Yuanhe River) to verify its practicability, reliability, and applicability. Results showed that the optimal pretreatment conditions were as follows: water samples were acidified to pH 3.0, added with 0.2 g Na2EDTA for metal ion chelation, enriched using Oasis® HLB cartridges at a loading flow rate of 8–10 mL/min, and dried for 5–30 min until no obvious liquid dripped from the cartridge tip, followed by elution with 12 mL of 0.1% (V:V) formic acid in methanol. Under these conditions, the spiked recoveries of 20 antibiotics in ultrapure water were generally above 80%, and most antibiotics exhibited recoveries exceeding 90%. In addition, the spatial distribution of antibiotic concentrations in the Poyang Lake watershed followed the following order: Jinjiang River > Yuanhe River > Ganjiang River > Poyang Lake. Sulfonamides, especially sulfamethoxazole with a maximum concentration of 250.08 ng·L−1, were identified as the predominant pollutants in this basin.