Application of Solid Phase Micro-Extraction (SPME) to the analysis of pesticide residues in vegetables

Solid Phase Micro-Extraction (SPME) is a new analytical technique, based on capturing the analytes by adsorption onto an organic phase coating a glass fibre, and subsequent direct desorption into the injector of a gas chromatograph. This technique has been successfully applied in the analysis of organic contaminants in water, giving linear responses and, in some cases, high sensitivities.The present paper reports data about the application of SPME to the analysis of pesticide residues in a vegetable matrix, testing over nearly one hundred active compounds, with two types of adsorbent phase (polydimethylsiloxane and Carbowax/divinylbenzene). A vegetable matrix spiked with pesticides was analyzed by SPME and by a traditional multi-residue method; recoveries were determined and compared for the two cases. The behaviour of the analytical response by SPME was studied in the range 0.01-1mg/kg by adding increasing amounts of given pesticide mixtures to the vegetable matrix.The procedure was further tested by analyzing real samples, and gave some difficulties in recovering the whole amount of some of the residues present (in comparison with the traditional method). The SPME method was then improved by pre-extracting with acetone and sonicating before the extraction/adsorption step. The results obtained were satisfactory (some certified matrices were also tested) with good accordance between the two methods. Nevertheless some active compounds showed very low responses or remained undetectable by SPME in our experimental conditions.