Sample processing and preparation optimisation with three different solvents for the residual analysis of 310 pesticides in three herbal plants by LC-MS/MS

In this study, sample processing and preparation conditions, including the selection of a proper extract solvent between ACN, EtAC, and its mixture, were optimised for the residue analysis of a large number of pesticides in different herbal plants (fennel seed, camomile, and dry mint). The number of pesticides that had acceptable accuracy and precision measurements using a mixture of ACN/EtAC in fennel, camomile, and dry mint (DM) was 298, 288, and 78, respectively. All these samples were processed to large particle sizes (routine processing). Together with the obtained scanning electron microscope images, these results showed that DM is one of the most troublesome herbal commodities for pesticide residue analysis. Besides, pesticide residue analysis in DM using the original QuEChERS (ACN) was not satisfactory (low recoveries, high precisions, and strong matrix effects). This situation becomes much worse when using EtAC. However, after optimising the sample processing and preparation steps with ACN and ACN/EtAC, satisfactory results for pesticide residue analysis in DM were obtained; a little better result was obtained when using ACN. A full validation was carried out using ACN, with applying the optimised sample processing and preparation steps, in DM at 10, 50, and 250 mu g/kg. The number of pesticides that have acceptable recovery and precision at these concentrations was 234, 299, and 310, respectively. Finally, the developed method was applied for pesticide residue analysis in 50 DM samples.