Citrus fruits and their by-products such as concentrated juices and essential oils are important intermediate by-products in the food industry that can selectively accumulate plant protection agrochemicals employed in their production. They are very difficult matrices for pesticide residue analysis due their high number and concentration of phytochemicals that could hamper the determinations. The fruit processing leads to the concentration/dilution or elimination of some of these natural products that change totally the nature of the matrix where the pesticides partition unevenly. Looking at the industrial process of the fruit, a unified vision for the pesticide residues analysis throughout the lemon fruit chain production, useful for the routine analysis of the above mentioned three matrices is presented. The driven concept is the minimization of matrix effects through sample dilution of the concentrated by-products, either after sample treatment or not. This approach will contribute to the maintenance of the whole instrumental system. QuEChERS AOAC 2007.01 was selected as the most suitable protocol for routine determination of, residues of 16 the pesticides most commonly used in the fruits during the citrus production through liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The same protocol was applied for pesticide residue analysis in concentrated juice after diluting 4 times the sample to minimize the matrix effects. For the analysis of lemon essential oils, the dilution and shoot procedure proved to be useful for LC-MS/MS and gas chromatography-mass spectrometry determination. The three methodologies were validated following SANTE guidelines, with quantitation limits below the established European Union and Codex Alimentarius maximum residue limits. The developed methodologies are useful tools for the routine control analysis of pesticide residues in lemon matrices, allowing high sample throughput and enhancing labs productivity.

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