Use of ultra-high-pressure liquid chromatography-quadrupole time-of-flight MS to discover the presence of pesticide metabolites in food samples.

In this paper we illustrate the use of two different methodologies to investigate the presence of pesticide metabolites in parent pesticide-positive food samples, using ultra-high-pressure liquid chromatography coupled to hybrid quadrupole time-of-flight (UHPLC-QTOF) mass spectrometry. First, a common fragmentation pathway between the parent pesticide and its metabolites has been considered to search for metabolites in two positive market samples (imazalil in lemon, chlorpyrifos in grape). Secondly, olive oil samples from field residue trials were used for automated application of comparative software (MetaboLynx), which was used with treated and untreated samples to search for expected and unexpected metabolites of phosmet. One of the main objectives when using these approaches was to avoid the tedious manual searching for potential metabolites within the huge amount of information contained in the total ion chromatogram acquired by TOF MS. The common fragmentation approach applied to TOF MS full-acquisition data, considering an enhanced fragmentation in the collision cell, has allowed the discovery of two metabolites of imazalil (1-[2-(2,4-dichlorophenyl)-2-hydroxyethyl]-1H-imidazole and 1-[2-(2,4-dichlorophenyl)-2-oxoethyl]-1H-imidazole) in a lemon positive sample, as well as another two metabolites of chlorpyrifos (chlorpyrifos-oxon and 3,5,6-trichloro-2-pyridinol) in a grape positive sample. Moreover, MetaboLynx application to TOF MS data, without promoting fragmentation, from treated and untreated olive oil samples has been helpful in detecting the metabolite phosmet-oxon. In both strategies, every metabolite detected by TOF MS was confirmed using QTOF and/or triple quadrupole instruments. Accurate masses given by TOF MS together with the valuable information on product ions given by QTOF MS/MS experiments were crucial for the unambiguous identification of metabolites.