Simultaneous Determination of Residues of Fluoroquinolone and Nitroimidazole Antibiotics in Bean Sprouts by Ultra- High Performance Liquid Chromatography- Tandem Mass Spectrometry

An aliquot (5 g) of bean sprout sample was taken, and mixed with 40 μL of 100 μg·L^-1 mixed internal standard solution and 10 mL of acetonitrile solution containing 1% (volume fraction, the same below) acetic acid. The mixture was shaken for 3 min, ultrasonicated for 20 min, and centrifuged for 3 min. The extraction process was repeated once, and the supernatant was combined, and diluted to 25 mL with acetonitrile solution containing 1% acetic acid. An aliquot (10.00 mL) was taken and placed into a centrifuge tube containing QuEChERS adsorbents composed of 100 mg of PSA, 100 mg of C₁₈ and 800 mg of anhydrous magnesium sulfate. The mixture was centrifuged for 3 min and settled for 5 min, and 5.00 mL of the supernatant was taken and blown to near dryness by nitrogen at 40 ℃. The residue was redissolved by 1.00 mL of 30% (volume fraction) acetonitrile solution containing 0.1% (volume fraction, the same below) formic acid, and the solution was passed through a 0.22 μm filter membrane. The filtrate was introduced into the ultra-high performance liquid chromatograph-triple quadrupole mass spectrometer for analysis. Twelve antibiotics were separated on ACQUITY UPLC HSS T₃ column (100 mm×2.1 mm,1.8 μ m) with mixed solutions composed of 0.1% formic acid solution containing 2 mmol·L^-1 ammonium formate and acetonitrile solution containing 0.1% formic acid at different volume ratios by gradient elution, ionized by ESI⁺ mode, detected by MRM mode, and quantified by internal standard method. As shown by the results, linear relationships between values of the mass concentration of 12 antibiotics and the peak area ratio were kept in the range of 1.0-250.0 μg·L^-1, with detection limits (3S/N) in the range of 0.079 6-0.494 μg·kg^-1. Test for recovery was made by standard addition method, giving results of recovery in the range of 71.6%-90.9%, and RSDs (n=6) of the determined values ranged from 1.5% to 7.6%. The proposed method was applied to the analysis of 160 batches of bean sprout samples (including soybean sprouts, mung bean sprouts and bean sprout seedings), and enrofloxacin, ciprofloxacin and metronidazole were detected in the first two samples with detection amounts in the range of 1.68-992 μ g·kg^-1.