Rapid determination of organophosphorus pesticides in onion and welsh onion by homogenization of frozen sample in dilute phosphoric acid

A simple and rapid method for the simultaneous determination of 30 kinds of organophosphorus pesticides in onion and welsh onion was developed. First of all, the sample to be analyzed was frozen to inactivate enzymes. The sample was cut into pieces, placed in a mixer cup containing dilute phosphoric acid and then homogenized. Pesticides in the homogenized sample were extracted with aqueous acetone. The extract was concentrated in vacuo, diluted with NaCl solution and reextracted with hexane. The pesticides were determined by gas chromatography with a flame photometric detector using the capillary column of ULBON HR-1. No interfering peak was found on the gas chromatograms of onion and welsh onion extracts. The recoveries of pesticides from onion and welsh onion at levels of 0.1μg/g were more than 77%, except for DDVP. The recoveries of DDVP were 60%. The detection limits of pesticides ranged from 0.003 to 0.04μg/g.