Combined target and post-run target strategy for a comprehensive analysis of pesticides in ambient air using liquid chromatography-Orbitrap high resolution mass spectrometry

Abstract

A comprehensive strategy for the analysis of current airborne pesticides has been developed using liquid chromatography coupled to high resolution mass spectrometry. The methodology includes both quantitative target analysis and post-run target screening analysis. The quantitative method was validated after a previous statistical optimisation of the main factors governing the ion source ionization and a study of the single-stage Orbitrap fragmentation through the HCD cell. The quantitative method presented recoveries ranging from 73 to 116%, with precision (RSD) lower than 20%, for the 35 substances in the scope of the target method. The full-scan accurate mass data were acquired with a resolving power of 50000 FWHM (scan speed, 2Hz), and alternating two acquisition events, ESI+ without fragmentation and ESI+ with fragmentation. The method-LOQ was 6.5pgm−3 for most of the target pesticides. For post-target screening a customized theoretical database, that included pesticides, metabolites and other substances such as emerging flame retardants was built up. For identification, accurate exact mass with less than 5ppm, and some diagnostic ions including isotopes and/or fragments were used.The strategy was applied to ten samples collected in a rural area of Valencia (Spain). Four pesticides, namely carbendazim, metalaxyl, myclobutanil and terbuthylazine, were detected in concentrations from 16pgm−3 to 174pgm−3. Some pesticides and metabolites (endothal, fenfuram, terbuthylazine-2-OH), in addition to two flame retardants were tentatively identified in the post-run target screening analysis.