Application of high-performance liquid chromatography–tandem mass spectrometry with a quadrupole/linear ion trap instrument for the analysis of pesticide residues in olive oil

This article describes the development of an enhanced liquid chromatography–mass spectrometry (LC–MS) method for the analysis of pesticides in olive oil. One hundred pesticides belonging to different classes and that are currently used in agriculture have been included in this method. The LC–MS method was developed using a hybrid quadrupole/linear ion trap (QqQLIT) analyzer. Key features of this technique are the rapid scan acquisition times, high specificity and high sensitivity it enables when the multiple reaction monitoring (MRM) mode or the linear ion-trap operational mode is employed. The application of 5 ms dwell times using a linearly accelerating (LINAC) high-pressure collision cell enabled the analysis of a high number of pesticides, with enough data points acquired for optimal peak definition in MRM operation mode and for satisfactory quantitative determinations to be made. The method quantifies over a linear dynamic range of LOQs (0.03–10 μg kg−1) up to 500 μg kg−1. Matrix effects were evaluated by comparing the slopes of matrix-matched and solvent-based calibration curves. Weak suppression or enhancement of signals was observed (<15% for most—80—of the pesticides). A study to assess the identification criteria based on the MRM ratio was carried out by comparing the variations observed in standard vs matrix (in terms of coefficient of variation, CV%) and within the linear range of concentrations studied. The CV was lower than 15% when the response observed in solvent was compared to that in olive oil. The limit of detection was ≤10 μg kg−1 for five of the selected pesticides, ≤5 μg kg−1 for 14, and ≤1 μg kg−1 for 81 pesticides. For pesticides where additional structural information was necessary for confirmatory purposes—in particular at low concentrations, since the second transition could not be detected—survey scans for enhanced product ion (EPI) and MS3 were developed.