ChemicalStudy of Pesticides in Kale Leaf (Brassica oleracea var. <i>Acephala</i>)by MALDI-MS

With increasing agricultural activities, vegetables such as kale are increasingly exposed to agrochemical substances. This study developed a method for monitoring pesticides present in kale leaves by direct analysis using mass spectrometry (MS) with laser desorption ionization (LDI) and matrix-assisted LDI (MALDI) sources. The MALDI was optimized by varying the concentration and application form (mixture or sandwich) of the 2,5-dihydroxybenzoic acid (DHB), α-cyano-4-hydroxycinnamic acid, and 2-mercaptobenzothiazole matrices. Our results suggest a better ionization efficiency in MALDI MS when the DHB matrix is used at a low concentration (0.050 mg mL^–1) and applied as a mixture. It was possible to detect seven of the 10 pesticides studied with total ion currents (TIC) of >10⁶ in most cases. This performance proved to be superior to the LDI MS approach.