The residue levels of chlorpyrifos in soybeans during storage and processing were investigated. Soybeans
were treated with chlorpyrifos aqueous solution and placed in a sealed plastic container. The residue of
chlorpyrifos was determined in soybeans at six time points within 0 and 112 days during storage and oil
processing of the soybeans was conducted. The analysis of the residues of chlorpyrifos was carried out by
gas chromatography–mass spectrometry (GC–MS). Results show that the dissipation of chlorpyrifos in
soybeans is about 62% during the storage period. Moreover, the carryover of the residues from soybeans
into oil is found to be related to the processing methods. Processing factor, which is defined as the ratio of
chlorpyrifos residue concentration in oil sample to that in the soybean samples, was 11 and 0.25 after
cold and hot pressing, respectively.