Determination of several cationic pesticides in food of plant and animal origin using the QuPPe method and ion chromatography with tandem mass spectrometry.

Several highly hydrophilic pesticides and metabolites are either permanently cationic or become cationic at low pH value. This makes them particularly suited for the analysis by ion chromatography (IC), especially since the suppressor technique enables a safe and reliable connection of IC with tandem mass spectrometry (IC-MS/MS). Here, we present a multi-method for the determination of 16 cationic pesticides using the 'quick polar pesticides' (QuPPe) extraction procedure and IC-MS/MS. The method covers permanently cationic compounds like chlormequat, mepiquat, diquat, and paraquat, as well as ionizable compounds like nicotine. Two different cation exchange columns were evaluated. Also, the impact of infusing an organic make-up solvent (e.g. acetonitrile and methanol) to the LC eluate between column exit and ion source entrance was tested at different infusion ratios, with acetonitrile performing best overall in terms of signal enhancements. Moreover, matrix effects tested with different types of matrices proved to be less problematic (±20 % in most cases) compared to LC-MS/MS methods. The final method was successfully validated at low levels in food of plant and animal origin (raspberry, sesame, rice, milk) and its suitability was verified by analysing >100 samples with incurred residues.