Determination of Residues of 6 Antibiotics in Soil by High Performance Liquid Chromatography Tandem Mass Spectrometry with Automatic Accelerated Solvent Extraction

The representative soil samples (about 1 kg) were randomly selected and divided into four parts, about 200 g of which was air dried, pulverized and sifted. 10.0 g of the above soil sample was taken into the extraction pool, and 15.0 g of diatomite was added. After mixing evenly, accelerated solvent extraction (ASE) was carried out, and the extract was purified by a gel purification system. 10 mL of the purified solution was taken and blown to nearly dryness at 50 ℃ by nitrogen. The residue was dissolved in 1 mL of methanol and the solution was passed through 0.22 μm filtration membrane. 6 antibiotics including lincomycin, clindamycin, lomefloxacin, pefloxacin, ennofloxacin and ciprofloxacin were determined by high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). Multiple reaction monitoring mode was used for MS analysis. As shown by the results, linear relationships between the values of corresponding peak area and mass concentration of 6 antibiotics were found in the range of 0.001-1.0 mg·L^-1, with detection limits (3S/N) in the range of 0.004-0.019 μg·kg^-1. The single standard solution and the spiked sample solution were analyzed by this method, with RSDs (n=6) of the determined values less than 4.0%. Test for recovery was made by standard addition method, giving results in the range of 83.8%-105%. This method was applied to analysis of actual samples, and the detection amounts of 6 antibiotics were 15.7-221.6 μg·kg^-1.