MULTIRESIDUE DETERMINATION OF NONVOLATILE AND THERMALLY LABILE PESTICIDES IN FRUITS AND VEGETABLES BY THERMOSPRAY LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY

A multiresidue method using high-performance liquid chromatography/thermospray/mass spectrometry/selected ion monitoring (HPLC/TSP/MS/SIM) to determine 19 thermally labile and nonvolatile pesticides in fruits and vegetables was evaluated. The pesticides were extracted from apples, beans, lettuce, peppers, potatoes, and tomatoes with a slightly modified Luke multiresidue extraction procedure. Aldicarb, aldicarb sulfoxide, bufencarb, carboxin, chlorbromuron, diuron, linuron, methiocarb, methomyl, metobromuron, monuron, neburon, oxamyl, propoxur, and thiodicarb were analyzed by mass spectrometry in the positive ion mode. Fenvalerate, folpet, iprodione, and oryzalin were analyzed in the negative ion mode. The limits of detection of the pesticides in the crops were in range 0.025-1 ppm. For those 14 pesticides with limits of detection of 0.25 ppm and below, recovery studies were performed at the 0.5 ppm fortification level in each of the six crops. Recoveries were between 69 and 110%, except for carboxin, which was recovered between 33 and 54%. Coefficients of variation were between 1.4 and 23.6%, with an average of 9.05%.