A high-performance liquid chromatographic method for the determination of cypermethrin in vegetables and its application to kinetic studies after greenhouse treatment
1997
Metwally, M.E.S. | Osman, M.S. | Al-Rushaid, R.
A high-performance liquid chromatographic (HPLC) method was developed in our laboratory for the analysis of cypermethrin (CM) in authentic samples, in formulations, and in spiked vegetables. The method depends on the use of a reverse-phase C8 column coupled with either methanol/water or acetonitrile/water as mobile phase, and UV detection. The method was linear in the range 0.05-100 micrograms ml-1 CM in methanol with a regression coefficient (r) of 0.995 (+/- 0.03). In spiked vegetable samples, the method was linear in the range 0.05-10 micrograms g-1, with r > 0.95 for all vegetables, with a detection limit of 0.02 micrograms g-1. Preliminary investigations revealed the suitability of the HPLC technique for the analysis of the pesticide in formulations as well as in spiked vegetable samples. The recovery of CM spiked to cucumber, eggplant, green-pepper and tomato was 65% (+/- 3.8%), 63% (+/- 6.49%), 77% (+/- 4.29%) and 71% (+/- 5.95%), respectively. The method was utilized to study the disappearance kinetics of CM under field conditions. CM residue disappears following first-order kinetics in the four vegetables with first-order rate constants of -2.80 (+/- 0.32) X 10(-2) h-1 for cucumber, -1.06(+/- 0.21) X 10(-2) h-1 for eggplant, -0.81(+/- 0.12) X 10(-2) h-1 for pepper, and -0.66(+/- 0.12) X 10(-2) h-1 for tomato. The higher disappearance rate of the pesticide on cucumber is mainly due to the high growth rate of this fruit relative to the other fruits. The pre-harvest waiting period was calculated for each vegetable fruit at different application rates. At the regular application rate, the value ranged from 36 to 120 h depending on the type of the fruit, rate of disappearance of the pesticide and the maximum allowable limit.
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