Rapid Determination of Residues of Tetracyclines and Quinolones in Marine Fish by Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry with QuEChERS

An aliquot (1.00 g) of the homogenized sample was taken, and 100 μL of 500 μg · L⁻¹ mixed internal standard working solution was added. After mixing well by vortex, 2 mL of 0.1 mol·L⁻¹ Na₂EDTA solution was added, and the mixture was vortexed for 1 min. Then 8 mL of acetonitrile was added, and the mixture was vortexed for 1 min, sonicated for 15 min, and centrifuged for 3 min. All the supernatant was taken and placed into a Cleanert LipoNo purification tube for shaking for 1 min and settling for 1 min. All the supernatant was taken and blown to dryness by nitrogen at 45 ℃. The residue was re-dissolved in 1.0 mL of 0.1% (volume fraction, the same below) formic acid-acetonitrile solution at volume ratio of 95∶5. The solution obtained was passed through a 0.22 μm organic filter membrane, and 4 tetracyclines and 5 quinolones in the filtrate were determined by ultra-high performance liquid chromatography-tandem mass spectrometry. In chromatographic analysis, ACQUITY UPLC^® BEH C₁₈ chromatographic column was used as the stationary phase, and mixed solutions of 0.1% formic acid solution and acetonitrile at different volume ratios were used as the mobile phase for gradient elution. In mass spectrometry analysis, the positive ion (ESI⁺) mode of the electrospray ion source was used for ionization, multiple reaction monitoring (MRM) mode was used for scanning, and the isotope internal standard method was used for quantification. It was shown that linear relationships between values of the mass concentration ratio and peak area ratio of 4 tetracyclines and 5 quinolones to the internal standard were kept in the range of 5.00-125 μg·L⁻¹, with detection limits of 2.00 μg·kg⁻¹. Test for recovery was made according to the standard addition method, giving recoveries in the range of 91.3%-110%, and RSDs (n=6) of the determined values ranged from 3.4% to 11%. The proposed method was used for the analysis of 200 batches of marine fish samples, and the detection results were basically consistent with those given by the national standards,with lower pre-treatment time and number of personnel involved.