Determination of Residues of 7 Commonly Used Pesticides in Paddy Water by Liquid Chromatography-Tandem Mass Spectrometry Combined with Automatic Solid Phase Extraction

Paddy water samples were randomly collected, floating debris in which was removed. An aliquot (1 000 mL) was taken, and its acidity was adjusted to neutral. An aliquot (500 mL) of the above water sample was taken and passed through the activated HLB solid phase extraction column at flow rate of 12 mL·min^-1, and elution was made with 15 mL of acetone-cyclohexane mixed solution at volume ratio of 2:1. The eluate was collected, and blown to near dryness by nitrogen at 45℃. Acetonitrile of 1 mL was added to dissolve the residue, and the mixed solution was analyzed by liquid chromatograph-triple quadrupole tandem mass spectrometer. In chromatographic analysis, YMC sphere ODS C₁₈ chromatographic column was used as the stationary phase, and mixtures composed of methanol and 0.1% (volume fraction) formic acid solution at different volume ratios were used as the mobile phase for gradient elution. In the MS analysis, the ESI⁺ mode was used for ionization, and the MRM mode was used for detection. It was shown that linear relationships between values of the mass concentration and the corresponding peak area of 7 pesticides including thiazinone, imidacloprid, carbendazim, tricyclazole, isoprothiolane, bensulfuron methyl and acetochlor, were kept in the same range of 0.01-4.00 mg·L^-1, with detection limits (3S/N) in the range of 0.006-0.028 μg·L^-1. The spiked recovery test was conducted on blank water samples at the 3 concentration levels, giving recoveries ranging from 85.2% to 103%, and RSDs of the determined values were less than 5.0%.