Analysis of pesticides in nuts by online reversed-phase liquid chromatography-gas chromatography using the through-oven transfer adsorption/desorption interface.

A new method to determine pesticide residues in nuts is presented, in which the pesticides are extracted from samples with a small amount of ethyl acetate and anhydrous sodium sulfate. No additional cleanup or concentration steps are necessary. The extract is directly injected into the high-pressure liquid chromatograph, where preseparation of the pesticide residues from other components coextracted from the nuts is carried out using methanol/water as the eluent. The selected liquid chromatography fraction containing the pesticides is automatically transferred to the gas chromatograph using the through-oven transfer adsorption/desorption interface. The calculated limits of detection for each pesticide varied from 0.1 to 61.3 microg/kg. The repeatabilities of the analysis and the overall procedure (extraction and analysis) were satisfactory. No variations in the retention time were observed. The method was applied to the analysis of pistachio nut, peanut, walnut, hazelnut, and sunflower seed.