Determination of Residues of 3 Antimicrobial Fungicides in Crop Soil by High Performance Liquid Chromatography-Tandem Mass Spectrometry with Fully Automatic QuEChERS Purification

A method for determination of residues of 3 antimicrobial fungicides in crop soil, including chunlei mycin, multi anti mycin, and blades, was proposed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) with fully automatic QuEChERS purification. The crop soil samples were crushed by a grinder, and stored at −18 ℃. 25 g of the processed crop soil sample was taken, and placed in the sample tube equipped with the QuEChERS automatic sample preparation system. One ceramic homogeneous proton, 20 mL of 85% (volume fraction) methanol solution, QuEChERS extraction kit, and internal tube (containing purification agent) were added respectively. The mixture was shaken at a rotational speed of 2 000 r·min⁻¹ for 5 min, and centrifuged at a rotational speed of 6 000 r·min⁻¹ for 5 min. 2 mL of purified solution was transfered into a test tube, and blown to near dryness by nitrogen at 50 ℃, and 1 mL of methanol was added for reconstitution. The solution was passed through a 0.22 µm filter membrane, and 3 antimicrobial fungicides in the filtrate were determined by HPLC-MS/MS. Waters BEH ODS C₁₈ column was usede as the stationary phase and the mixed solution composed of 0.1% (volume fraction) formic acid solution and acetonitrile at different volume ratios was used as the mobile phase for gradient elution. Electrospray ion (ESI) source was used for mass spectrometry. The targets were analyzed by multiple reaction monitoring (MRM) mode in positive ion（ESI⁺）scanning mode. As shown by the results, linear relationships between the corresponding quantitative ion response values and mass concentrations of 3 antimicrobial fungicides were found within 0.005-0.5 mg·L⁻¹, with detection limits (3S/N) in the range of 0.10-0.13 μg·kg⁻¹. Test for recovery was made by the standard addition method, giving results in the range of 83.2%-106%, with RSDs (n=6) of the determined values less than 5.0%. This method could be used to determine the residues of 3 antimicrobial fungicides in actual crop soils, and the detection amounts were in the range of 10.11-59.07 μg·kg⁻¹.