Simultaneous determination of multi pesticide residues in vegetables

The objectives of this experiment were to determine the accuracy (percentage recovery or PR) and precision (coefficient of variation or CV) of three different cleanup methods for the measurement of seven pesticides in different vegetables (turnip greens, dried beans and cabbage) using selective ion monitoring (SIM) on a gas chromatograph-mass spectrometer (GC-MS). The cleanup methods for an acetonitrile extract of the vegetables included (1) a Florisil solid phase extraction (SPE), (2) a double SPE using C₁₈ and amino propyl cartridges, and (3) a direct injection of the extract. The pesticides included ethalfluralin, bromoxynil, dimethoate, alachlor, bentazon, pendimethalin and esfenvalerate. The limits of detection for each pesticide in the acetonitrile extract of turnip greens also were determined.

Three of the pesticides, ethalfluralin, pendimethalin and esfenvalerate, were recovered at measurable amounts by methods 1 and 3, while dimethoate was recovered by methods 2 and 3, and alachlor was recovered by all methods in all vegetables. Ethalflluralin, alachlor, pendimethalin and esfenvalerate, were recovered at high enough percentages in method 1 to be measured in each vegetable, but method 2 should be used for quantitation of dimethoate. Although bromoxynil and bentazon could be measured by GC-MS SIM, neither one was recovered by any of the 3 methods from the acetonitrile extracts.

The CVs for the four pesticides in method 1 and for dimethoate in method 2 ranged from 5.6 to 38.4% and, overall, were of similar magnitudes as those reported by other researchers. The limits of detection of the pesticides in the turnip greens acetonitrile extract matrix ranged from 0.00075 (alachlor) to 0.19 ppm (dimethoate) and were, with the exception of dimethoate, lower than the limits of detection reported by others using SIM.