Agrotóxicos em óleos comestíveis: avaliação de procedimento de purificação de extrato empregando diferentes adsorventes e validação por UHPLC-MS/MS

Abstract

The goal of this study was to evaluate the efficiency of several adsorbents on fat removal from extracts of edible oil matrices (olive, soya and sunflower) during residue determination of 165 pesticides employing liquid chromatography coupled to mass spectrometry. The extraction procedure employed in this study was the citrate version of QuEChERS method and the first study carried out was evaluating the efficiency of low temperature precipitation step (freezing out) before clean-up step, both tested in olive oil. During clean-up evaluation, three different adsorbents were studied, where one of them was employed in two different ways, totalizing four different clean-up procedures: i) PSA in combination with magnesium sulfate (d-SPE); ii) Z-sep combined with magnesium sulfate (d-SPE); iii) Z-sep (cartridges SPE) and iv) EMR-Lipid (d-SPE). After evaluation of freezing out and clean-up procedures employing liquid chromatography coupled to high resolution mass spectrometry (UHPLC-QTOF-MS), the freezing out combined with clean-up by dispersive solid phase extraction using EMR-Lipid showed important advantages when compared to the other evaluated techniques, such better recovery rates and RSD%. The method was validated for olive, soya and sunflower oils employing ultra-high performance liquid chromatography coupled to mass spectrometry (UHPLC-TQ-MS/MS) at 10, 20 and 50 μg kg-1. Mean recovery for all evaluated levels in the three matrices was about 70% with mean RSD% below 11%. Most of the pesticides that showed recovery below 70% presented RSD% values lower than 10. For this reason, linearity and matrix effect studies were carried out employing procedural standard calibration approach, an alternative type of calibration that compensates low recovery values and matrix effect, in the range from 10 to 500 μg kg-1. From all evaluated pesticides, 93% showed determination coefficient equal to or higher than 0.99. Matrix effect was similar when the three oils were compared. The method was successfully applied on pesticides determination in oil matrices purchased in Almería and Murcia cities, located at southeastern of Spain.