Microwave/SPME method to quantify pesticide residues in tomato fruits

A new analytical method using focused microwave-assisted extraction (FMAE), coupled with solid phase micro-extraction (SPME), has been elaborated to determine 25 pesticides used in tomato cultivation. Microwave energy was used for a fast and controlled heating of solvent to selectively extract compounds. Calibration curves were plotted from blank tomato samples spiked at different concentrations with standards. A linear response was obtained between 10 and 1000 microg/Kg for pyrethroids and between 0.1 and 5000 microg/Kg for other compounds. For all studied substances, the resulting correlation coefficient (r(2)) was greater than 0.99. Limits of detection (LOD) and quantification (LOQ) were measured lower than 8 and 25 microg/Kg, respectively. The relative standard deviation (RSD) was determined below 15% for all pesticides. Field incurred tomato samples were used to validate the new FMAE/SPME method. Observed analysis results by using this technique were in good agreement compared to those obtained by two accredited trading laboratories using traditional methods. Four tomato samples, bought in a local market, were also tested with the FMAE/SPME method.