Nowadays, about 3000 essential oils are produced and used worldwide in various application fields related to pharmaceutical, agronomic, food and perfume industries. These oils are extracted from citrus or medicinal and aromatic plants. Due to the use of pesticides in plant cultivation, the presence of such residues cannot be ruled out. The variety of pesticides used and the widespread use of essential oils necessitate the development of a multi-residue analytical method to ensure consumers' health. The state of the art of analytical methods related to this issue has revealed a clear lack of performance both in terms of detection limit as well as in the number of analyzed pesticides. This manuscript proposes the development of a multi-residue analytical method of pesticides in essential oils by coupling liquid chromatography and mass spectrometry, technology which is, considering the bibliography, the best dedicated to answer this problematic. After demonstrating the performance of the new acquisition mode Scheduled SRM, available on the mass spectrometer 4000 QTrap, for the detection and quantification of 250 pesticides in a determined solvant, the importance of considering the nature of matrix in sample's preparation as well as during the sample's analysis has further been proved by the study of two representative essential oils (lavandin and lemon). Finally, the multi-residue LC-MS/MS analysis method has been applied to the research of pesticides in real essential oils. This method has demonstrated its ability to detect, quantify and identify pesticides in these matrices through the use of a coupled acquisition mode SRM-EPI making use of the hybrid mass spectrometer's specificities and especially its linear ion trap. Moreover this work has shown the importance of having such a method, considering the number of detected pesticides and their relatively high concentrations. These ones can indeed reach a level higher than one milligram per liter in the analyzed essential oils.
