The application of solid phase microextraction in the analysis of organophosphorus pesticides in a food plant

A SPME method for the determination of organophosphorus pesticide residues in a local food plant, Chrysanthemum coronarium, was established. Pesticide residues were extracted by SPME fiber (with 100 mu m poly(dimethylsiloxane) coating) from a biphasic water/plant tissues mixture and determined by GC-FPD. An equilibrium model was derived for the system and revealed that pesticide recoveries were related to the water:plant tissues ratio, f(r) and the partition coefficient, K(WV), for the distribution of pesticides between the aqueous phase and the plant tissues. The model was verified by four organophosphorus pesticides, namely phorate, diazinon, methyl parathion, and ethion. The best fitted K(WV) values (P < 0.05) for the pesticides were found to be 4.73 +/- 0.32 x 10(-2) (phorate); 1.11 +/- 0.10 x 10(-1) (diazinon); 9.18 +/- 0.95 x 10(-2) (methyl parathion); and 8.21 +/- 1.28 x 10(-3) (ethion). Remarkable correlation between the K(WV) of the organophosphorus pesticides and their octanol/water partition coefficients, K(OW), was also established.