The evaluation of matrix effects in pesticide multi-residue methods via matrix fingerprinting using liquid chromatography electrospray high-resolution mass spectrometry

Twenty-three different commodities were extracted using the QuEChERS method. Their natural compounds were mapped based on their retention time and accurate mass using liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS). In addition, repeated analyses of spiked samples were evaluated to understand the relationship between the matrix ions and ion suppression. The number, distribution and abundance of the natural components varied greatly between the matrices, even within the same commodity group. We considered complex matrices to be those providing a high number/ concentration of natural components along with high ion suppression (>50%). For example, leek contained more than 50% of pesticides with high ion suppression. Conversely, simple matrices such as tomato presented practically no pesticides (<5%) with high ion suppression. Injection amounts of 10 mL of the matrix extracts were evaluated containing 0.1 g mL(-1) of matrix equivalent (or lower) instead of the common values of 1 g mL(-1); this new proposed approach being an effective method to evaluate the reductions in interfering compounds and thus decreasing the problems associated with ion suppression. Finally, matrix fingerprinting studies on the accurate mass compounds obtained following the application of various extraction methods helped to determine the number and molecular weight of the co-extracted compounds, leading to the selection of the most suitable multi-residue extraction method. Such studies have evaluated the interest in the application of extraction methods and specific clean-up materials such as calcium chloride (CaCl2) in tea, or zirconium dioxide (ZrO2) in parsley analysis as a modification to the original QuEChERS method.