Comparison of microextraction procedures to determine pesticides in oranges by liquid chromatography-mass spectrometry

A liquid chromatographic-mass spectrometric method has been developed for the determination of bitertanol, carbendazim, fenthion, flusilazole, hexythiazox, imidacloprid, methidathion, methiocarb, pyriproxyfen and trichlorfon. Two procedures, based on stir bar sorptive extraction (SBSE) and matrix solid-phase dispersion (MSPD), have been evaluated for the extraction of these compounds in oranges. Their respective advantages and disadvantages are also discussed. The recoveries obtained by MSPD ranged from 47 to 96% and the relative standard deviations (RSDs) ranged from 1 to 15%, whereas with the SBSE method the recoveries were between 8 and 84% and the RSDs between 4 and 16%. Although, the limits of quantitation of most compounds are much better (0.001-0.05 mg kg(-1)) by SBSE, it is not suitable to determine some polar pesticides as carbendazim, imidacloprid and trichlorfon. Results obtained by both methods were compared, in terms of sensitivity and selectivity, with a classical ethyl acetate extraction method, and the three methods were applied to analyze real samples. As MSPD is easier to perform, faster than the organic solvent extraction, and shows equal accuracy and resolution, its application for analyzing pesticides in oranges is recommended. (C) 2002 Elsevier Science B.V. All rights reserved.