An analytical approach was developed to simultaneously determine 13 antibiotics in sulfonamides, quinolones, and macrolides in leafy vegetables by ultra-performance liquid chromatography coupled with triple quadrupole mass spectrometry (UPLC-MS/MS). After optimizing extracted solutions, purification methods, and eluents of antibiotics in vegetable substrates, and taking into account the influence of environmental changes and experimental conditions on the results, the optimal experimental scheme was determined. This involved ①weighing 500 mg of vegetable samples and adding 20 mL of methanol-Mcllvaine-Na2 EDTA solution; ② conducting ultrasonic and centrifugal extraction three times; ③ Allowing rotary evaporation to 20 mL to pass a HLB solid phase extraction column; ④ Eluting the extraction column using 6 mL of methanol, upon which the eluent was dried almost completely; ⑤ Re-dissolving the eluent with a mixed solution of acetonitrile:water (volume ratio of 2:8); ⑥ Detecting by UPLC-MS/MS after centrifugation and filtering. Phase A and B of UPLC-MS/MS used an aqueous solution of 1‰ formic acid and acetonitrile, respectively to conduct gradient elution. Results showed that when the pakchoi spiked at 300 ng·g-1, the spiked recoveries of 13 antibiotics were 38.05%-96.97%. At 150 ng·g-1, the spiked recoveries were 34.52%-111.10%. At 50 ng·g-1, the recoveries of standard addition were 41.75%-107.13%, and the relative deviation (RSD) values were all below 8.68%. The detection limit was 0.4-1 ng·g-1, and the limit of quantification was 1.5-3 ng·g-1. This demonstrated good extraction and recovery efficiency on different types of leafy vegetables, and presented a good analytical application effect. The antibiotic residues were detected in four kinds of leafy vegetables in found in markets. The total content ranged from 1.59 ng·g-1 to 32.01 ng·g-1, and the antibiotic content in samples was calculated by dry weight. The content of antibiotics in pakchoi was the highest, followed by Chinese cabbage, lettuce, and coriander. Among the antibiotics detected, sulfadimidine was the most abundant from the selected leafy vegetables. The content of antibiotics was very low, however the potential health risks caused by long-term consumption could not be ignored.
Keywords: antibiotics; detection methods; leafy vegetables; mass spectrometry; ultra-high performance liquid chromatography.