Characterization of MS/MS product ions for the differentiation of structural isomeric pesticides by high-resolution mass spectrometry

Authors: Nunez, Alberto; Sapozhnikova, Yelena; Lehotay, Steven

Submitted to: Toxics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2018
Publication Date: 10/2/2018
Citation: Nunez, A., Sapozhnikova, Y.V., Lehotay, S.J. 2018. Characterization of MS/MS product ions for the differentiation of structural isomeric pesticides by high-resolution mass spectrometry. Toxics. 6(4):59. https://doi.org/10.3390/toxics6040059 -.
DOI: https://doi.org/10.3390/toxics6040059

Interpretive Summary: Numerous pesticides are used in agriculture worldwide to protect crops and increase harvest yields. To protect consumer’s health, tolerances, or maximum residue limits (MRLs) are established and enforced by regulatory agencies around the world. Hence, reliable identification of pesticide residues in foods is of paramount importance in global food trade. Isomeric pesticides (i.e. pesticides with the same molecular formula and different atom arrangements) are widely used in agriculture and are challenging to differentiate for accurate identification. In this work, state-of-the art high-resolution mass spectrometry was applied to differentiate isomeric pesticides based on molecular formulas of produced ions, and ion formation pathways and ion structures were proposed. This information is valuable to reduce the rates of false positives in pesticide monitoring programs, as wrong results can have detrimental economic and health consequences.

Technical Abstract: Structural isomeric pesticides are used in agriculture and may be challenging to differentiate for accurate identification in pesticide monitoring programs. Because of structural similarity, isomeric pesticides are difficult or impossible to separate chromatographically, thus their accurate identification may rely solely on mass spectrometry analysis. In this study, we challenged the power of high resolution Q-Orbitrap mass spectrometer (MS) to produce and examine MS/MS product ions for the selected five pairs of isomeric pesticides from different classes: pebulate and vernolate, methiocarb and ethiocarb, uniconazole and cyproconazole, sebuthylazine and terbuthylazine, orbencarb and thiobencarb. The use of Q-Orbitrap MS with mass error <3 ppm allowed proposal of the product ion structures based on the ion formulae, data interpretation, and literature search. Unique product ions specific for pebulate, vernolate, methiocarb, ethiofencarb and uniconazole were observed. Elucidation of the observed MS/MS product ion structures was conducted, and the fragmentation pathways were proposed. This information is valuable to increase selectivity in MS/MS analysis, and differentiate isomeric pesticides to reduce the rates of false positives in pesticide monitoring programs.