Determination of Methyl-Pyrimithate and Ethyl-Pyrimithate in Garlic by Gas Chromatography and Gas Chromatography-Mass Spectrometry

10.00 g of the pounded and homogenized garlic sample were taken and extracted vortically with 3 mL of water, 20 mL of acetonitrile and 3 g of sodium chloride for 2 min. After centrifuging, 10.0 mL of the upper layer were taken and evaporated to near dryness at 40℃, and the residue was dissolved in 3 mL of CH₃OH-H₂O (1+5) solution, which contains φ 1% formic acid. The solution obtained was then purified by passing through SPE column. The analytes were adsorbed on the SPE column, and were eluted from the column by CH₃OH containing φ 0.5% of aq. ammonia. The eluates were collected and evaporated to near dryness by N₂-blowing at 40℃. The residue was dissolved with its volume made up to 1.0 mL by a mixture of acetone and n-hexane (1+9). Contents of methyl-pyrimithate and ethyl-pyrimithate in the solution were determined separately by GC-FPD and by GC-MS. Linear relationships between values of peak areas of the 2 analytes and their mass concentrations were obtained in definite ranges, with values of lower limits of determination (10S/N) of 0.01 mg·kg^-1 for GC-FPD and GC-MS. Recovery was tested by standard addition method, giving values of recovery in the ranges from 81.6% to 91.6% and from 94.4% to 98.1% for the 2 methods respectively, and RSDs (n=6) ranged from 4.1% to 8.6% and from 3.1% to 9.4%.