Determination of Residues of Diazinon and Chlorpyrifos in Lavender and Rosemary Leaves by Gas Chromatography.

A sensitive gas chromatographic (GC) GC method has been developed for the determination of diazinon and chlorpyrifos residues in lavender and rosemary leaves. The developed method consists of blending weighed samples of chopped leaves with sodium sulfate as the dehydrating agent, extraction with ethyl acetate, filtration, evaporation with a rotary evaporator, and, finally, capillary GC determination of the pesticides. The recoveries of the method were greater than 90%, and the LOQ was less than 0.1 µg/mL. The method was applied to determine the rate of disappearance of diazinon and chlorpyrifos from lavender and rosemary leaves pretreated with the studied pesticides. The half-life values (t1/2) of diazinon were found to be 5.93 and 6.35 days for lavender and rosemary leaves, respectively, whereas the t1/2 values of chlorpyrifos were calculated to be 7.86 and 9.52 days for lavender and rosemary leaves, respectively. The safe harvest interval (preharvest interval; PHI) was suggested to be after 21 and 24 days for diazinon and chlorpyrifos, respectively. The PHI refers to the amount of time that must lapse (in days) after a pesticide application before a crop can be cut.