Multiresidue screening of pesticides in fruits using an automatic solid-phase extraction system

About 20 pesticides were determined in lyophilized fruits using a semiautom atic multiresidue method, based on solid-phase extraction (SPE) with a sili ca column. The lyophilization of the sample, besides the SPE procedure sele cted, provided clean extracts despite the complexity of the matrixes studie d. In addition, the lyophilization process allows sample preservation for a t least three months without changes in the concentrations of the pesticide s. Determination and quantitation of organochlorine and pyrethroid residues was carried out using a gas chromatograph equipped with an electron captur e detector (GC-ECD), and a mass spectrometric detector (GC-MS) was used for confirmation purposes. Organochlorine pesticides provided average recoveri es (spiked at three concentration levels in eight different fruits) near 93 +/- 4%, being lower (89 +/- 8%) for pyrethroids as a consequence of their higher degradation and interaction with the sample matrix. On the other han d, the detection limits achieved for all pesticides (0.5-8 ng per g of lyop hilized fruit) allow their determination at the MRLs established by the Eur opean Union, with good precision (similar to5%). Finally, from the 100 diff erent fruits screened, only 10 positive responses were obtained, which were further confirmed by GC-MS.