Determination of 20 Antibiotics in Soil by Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry with Accelerated Solvent Extraction and Solid Phase Extraction

The method for determination of 20 antibiotics (including chloramphenicols, quinolones, sulfonamides, and tetracyclines) in soil by ultra-high performance liquid chromatography-tandem mass spectrometry with accelerated solvent extraction and solid phase extraction. After impurity removal, dehydration, freeze-drying, grinding and sieving, 2.0 g of soil sample was taken, and 4 g of diatomaceous earth and 20 μL of 1.00 mg · L⁻¹ mixed internal standard solution were added. The mixture was treated by accelerated solvent extraction with the mixed solution composed of acetonitrile and Na₂EDTA-Mcllvaine buffer solution (pH 4) at volume ratio of 1∶1. The extraction solution was collected and its acidity was adjusted to pH 3.0 before passing through the HLB solid phase extraction column. The column was rinsed by 10 mL of water, and eluted by 10 mL of the mixed solution of methanol and acetonitrile at volume ratio of 1∶1. The eluate was collected, and blown to near dryness by nitrogen, and its volume was made up to 1.0 mL with 10% (volume fraction) methanol solution. The solution was passed through a 0.22 μm filter membrane, and the filtrate was used for analysis by ultra-high performance liquid chromatograph-tandem mass spectrometer. In chromatographic analysis, the Kinetex C₁₈ column was used as the stationary phase, and the mixed solution of 0.1% (volume fraction) formic acid solution and methanol at different volume ratios was used as the mobile phase for gradient elution. In the mass spectrometry analysis, the electrospray ionization (ESI) source was used for ionization, the multiple reaction monitoring (MRM) mode was used for detection, and the internal standard method was used for quantification. It was shown that linear relationships between values of the mass concentration ratio and the peak area ratio of 20 antibiotics to internal standards were kept in the range of 0.50-250 μg · L⁻¹, with detection limits (3.143s) in the range of 0.10-0.55 μg · kg⁻¹. At the spiked concentration levels of 2.0, 10.0, 100 μg · kg⁻¹, recoveries of 20 antibiotics were found in the range of 60.0%-126%, and RSDs (n=6) of the determined values ranged from 4.0% to 19%. The proposed method was used for the analysis of 8 actual soil samples, and 10 antibiotics were detected with detection amounts ranging from 2.2 μg · kg⁻¹ to 75.6 μg · kg⁻¹.