Determination of Phorate and Its Metabolites Residues in Vegetable Soil by Ultra-High Performance Liquid Chromatography-Quadrupole/ Electrostatic Field Orbitrap High Resolution Tandem Mass Spectrometry

A method for determination of residues of phorate and its 5 metabolites (phorate sulfone, phorate sulfoxide, phorate oxon, phoratoxon sulfone and phoratoxon sulfoxide) in vegetable soil by ultra-high performance liquid chromatography-quadrupole/electrostatic field orbitrap high resolution tandem mass spectrometry. Targets in sample were extracted with acetonitrile solution containing 1% (φ) acetic acid by vortex, and sodium chloride was added for salting out. After centrifuging, the supernatant was purified with ethylenediamine-N-propylsilane (PSA) and centrifuged subsequently. The supernatant was passed through 0.22 μm organic filter membrane. The targets in the filtrate were fixed with a CAPCELL CORE AQ chromatographic column and mixed solutions composed of 0.1% (volume fraction, the same below) formic acid solution (containing 5 mmol·L^-1 ammonium formate) and methanol solution (containing 0.1% fromic acid and 5 mmol·L^-1 ammonium formate) with various volume ratios were used for gradient elution. Quadrupole/electrostatic field orbitrap high resolution tandem mass spectrometer was adopted for detection in the positive ion mode and parallel reaction monitoring (PRM) mode of the heated electrospray ion source, and mixed standard solution series prepared by matrix matching method were used for making the working curves. The results showed that mass concentrations of the 6 pesticides were in linear relationships with their corresponding peak areas within certain ranges, and lower limits of determination (10S/N) were found in the range of 0.10-10 μg·kg^-1; the spiked recovery test was made on actual samples at 3 concentration levels, giving values of recovery in the range of 90.2%-109%, and RSDs (n=5) of the determined values were ranged from 0.33% to 10%; the proposed method was used for the analysis of 39 vegetable soils samples, and targets were detected in two samples, phorate and phorate oxon were not detected, and the detected amount of phorate sulfone was relatively high (8.09, 8.55 μg·kg^-1).