Determination of Pesticide Residues in Olive Oil Using QuEChERS Extraction and Liquid Chromatography-Orbitrap High-Resolution Mass Spectrometry: Comparison of Different Clean-Up Sorbents and Validation Study

The aim of this study was the optimization of the clean-up step in the widely applied QuEChERS method for the determination of 39 representative multiclass pesticides in olive oil with Ultra-High-Performance Chromatography-Orbitrap Mass Spectrometry (UHPLC-Orbitrap-MS). The analytical methodology combines the original version of QuEChERS extraction with two different clean-up-step approaches, using firstly a combination of Z-Sep(+), PSA and MgSO4 and secondly EMR-lipid. The methods were compared for their efficiency in the removal of fats and co-extractives and their effect on the analytical performance characteristics. Both methods were evaluated in terms of linearity, matrix effects (ME), recovery, precision, limits of detection (LOD) and quantification (LOQ) and expanded uncertainty in three spiking levels of 30, 100 and 300 mu g/kg. The recoveries ranged between 70-113% for 95% of analytes (RSDr < 14%) when EMR-lipid was used as a sorbent, while in the case of Z-Sep(+)/PSA/MgSO4 recoveries ranged between 72-107% for 92% of analytes (RSDr < 18%). ME showed low signal suppression for 77% of analytes in the case of Z-Sep(+)/PSA/MgSO4 and for 85% of analytes in the case of EMR-lipid. According to the results, both methodologies provided good analytical performances fulfilling validation criteria; however, the EMR-lipid sorbent showed better clean-up capacity (i.e., less matrix effects and lower variability in extraction recoveries) and validation parameter values for more analytes. The validated method was successfully applied to 30 olive oil samples from different regions of Greece. No residues have been identified in the analyzed samples.