One-year routine application of a new method based on liquid chromatography-tandem mass spectrometry to the analysis of 16 multiclass pesticides in vegetable samples.

An analytical procedure has been developed for determining a group of 16 multiclass pesticides most commonly used in crop protection. The extraction step is performed with a mixture of ethyl acetate and sodium sulphate, in the presence of 6.5 M NaOH. After evaporation, a final extract containing 1 mg sample/ml extract, is obtained in methanol. Analysis of the methanolic extract, without additional clean-up steps, is performed by liquid chromatography-electrospray ionisation-tandem mass spectrometry combining positive and negative ion mode. The analytical performance of the method has been validated for three different matrices: pepper, lettuce and aubergine. Mean recoveries obtained were between 70 and 110% in most of the cases with a precision of <28%. Linearity of response over 2 orders of magnitude was demonstrated (r > or = 0.99) with limits of detection < or = 0.01 mg/kg in all the cases. No significant matrix effects were observed with the exception of triflumizol that presented a drastic decrease in response as a consequence of an ion formation suppression effect in the presence of pepper matrix. The method has been applied to the analysis of 560 vegetable samples, as a part of the monitoring programme of the Association of Producers and Exporters of Fruits and Vegetables of Almería (COEXPHAL). The unambiguous confirmation of the positive findings by comparison of the product ion mass spectra of the peaks in samples and standards, demonstrated the applicability of the method in routine analysis.