Multiplexed analysis of 215 pesticides with using scout-MRM

LC-MS-MS combined with Selected Reaction Monitoring (SRM) mode is a gold standard method to assay pesticides. As the number of targets increases, specific analyte transitions are monitored only around their expected retention time (RT) in order to ensure correct definition of peak shape. In this case, the analysis is secured applying RT windows much larger than the peak width to as far as possible take into account RT drift. However, any additional, even minor, modification of the LC configuration (extra-column volume change, flow rate, column length or diameter…) requires adjustment of this RT window. Because of independency towards RT, the new scout-MRM software alleviates all these limitations and expands the multiplexing capability as exemplified by multi-residue analysis of 215 pesticides. A multiplexed assay was build for 215 pesticides (174 from AB Sciex standard kit and 41 from IRSTEA, Lyon, France). LC-MS/MS was performed using Agilent 1290 system coupled to a QTRAP® 6500 system equipped with a TurboV® source. Separation was achieved on a C18 reverse phase column (Xbridge, 2.1x100x3.5µm) using a linear gradient consisting of A: water with 2mM ammonium formate and 0.05% formic acid and B: methanol with 2mM ammonium formate and 0.05% formic acid. Data were acquired with a modified version of Analyst® 1.6.2 software to implement scout-MRM. In the context of multi-residue pesticide assay, this preliminary study focused on the merit of new scout-MRM software towards other multiplexed monitoring modes in term of repeatability and accuracy. Scout signals are played by 5 spiked-in deuterated pesticides triggering 5 groups of transitions (2 transitions per pesticide, 430 transitions at all). Repeatability of scout-MRM and scheduled-MRM methods were assessed by calculating CVs from triplicate analysis of the 174 pesticide mix standard. Average CVs is about 3% for both methods, showing that they have equivalent performances. Finally, scout-MRM was used for multi-residue screening and quantification of pesticides in true surface water samples by applying an external calibration procedure. Accuracy of scout-MRM quantification results was ultimately compared to ones obtained with conventional scheduled-MRMTM approach.