Determination of 11 Quinolones Residues in Soy Products by High Performance Liquid Chromatography-Tandem Mass Spectrometry

The sample uniformly prepared (5.00 g) was extracted ultrasonically for 15 min with Na₂EDTA-Mcllvaine buffer solution, purified by Oasis PRiME HLB solid phase extraction column. The eluate was blown by nitrogen until nearly dry at 45 ℃, and the residue was dissolved with 2.0 mL of a mixture of 5 mmol·L^-1 ammonium acetate solution containing 0.1% (φ, the same below) formic acid and acetonitrile at the volume ratio of 9∶1, and filtered by the 0.22 μm aqueous phase filtration membrane. The 11 quinolones residues in the sample solution were determined by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). ZORBAX Eclipse plus C₁₈ column (100 mm×2.1 mm, 3.5 μm) was used as stationary phase, and a mixture of 5 mmol·L^-1 ammonium acetate solution containing 0.1% formic acid and acetonitrile at different volume ratios was used as mobile phase for gradient elution. Multiple reaction monitoring (MRM) mode via positive electrospray ionization was adopted in MS/MS analysis. The working curves of matrix matched mixed standard solution series were drawn, and isotope internal standard method was used for quantitative analysis. As shown by the results, linear ranges of these working curves for 11 quinolones were 0.5-400.0 μg·L^-1, with detection limits (3S/N) in the range of 0.2-0.3 μg·kg^-1. Test for recovery was made on blank samples at the 3 concentration levels by standard addition method, giving results in the range of 72.2%-119%, with RSDs (n=6) of the determined values in the range of 2.6%-9.7%. Samples of 58 batches were determined by this method, and none of 11 quinolones were found in these samples.