Selectivity enhancement using sequential mass isolation window acquisition with hybrid quadrupole time-of-flight mass spectrometry for pesticide residues

The introduction of sequential mass isolation window acquisition mode in high-resolution quadrupole time-of-flight analysers undoubtedly represents an important improvement in the MS/MS spectra obtained when working in non-target analysis. However, the advantages and limitations of this approach have not been sufficiently defined and evaluated. The present work seeks to fill this gap by considering its application in non-target multiresidue pesticide analysis. This work focuses on the called SWATH® method, which combines both MS and MS/MS acquisition, dividing the entire mass range into smaller segments for the MS/MS mode. The effect of the number of mass isolation windows, the total cycle-time lapsed, the sensitivity obtained, the MS/MS spectra quality, the ion ratio stability as well as the identification and quantification capabilities has been evaluated. The use of ten mass isolation windows for data acquisition was selected as a compromise between the required points per chromatographic peak and the reduction in interferences achieved. An identification study was carried out on 141 pesticides in 20 vegetable matrices to check the false positives and false identifications found automatically, in accordance with the criteria set out in Document No. SANTE/11945/2015. Furthermore, special attention was given to certain issues that can make correct identification difficult, such as low fragment abundance due using of a generic collision energy, the matrix influence on the collision cell, the effect of the concentration level as well as deconvolution failure and mass window width. Finally, to verify the efficiency of the optimum parameters proposed, two proficiency samples were analysed, obtaining good results. This proved the benefits in terms of identification and quantification purposes.