Development and Application of a High-Precision Algorithm for Nontarget Identification of Organohalogens Based on Ultrahigh-Resolution Mass Spectrometry

Brominated and/or
chlorinated organic compounds (referred to as
organohalogens) are frequently detected in natural and engineered
environments. However, ultrahigh-resolution mass spectrometry (UHR-MS)-based
nontargeted identification of organohalogens remains challenging because
of the coexistence of a vast number of halogenated and nonhalogenated
organic molecules. In this study, a new algorithm, namely, the NOMDBP
code, was developed to simultaneously identify organohalogens and
non-organohalogens from the UHR-MS spectra of natural and engineered
waters. In addition to isotopic patterns, for the first time, three
optional filter rules [i.e., selection for minimum
nonoxygen heteroatoms, inspection of the presence of newly formed
halogenated disinfection byproducts (Xn-DBPs), and of their precursors]
were incorporated into our code, which can accurately identify DBP-associated
peaks and further elucidate Xn-DBP generation and transformation mechanisms.
The formula assignment ratio against 2815 previously reported organohalogens,
and their 11,583 isotopologues exceeded 97%. Application of our algorithm
to disinfected natural organic matter indicated that oxygen-containing
Xn-DBP species accounted for a majority of the Xn-DBPs. Furthermore,
brominated Xn-DBPs (Br-DBPs) were characterized by a higher degree
of unsaturation compared to chlorinated Xn-DBPs. In addition to electrophilic
substitution and electrophilic addition reactions, the decomposition/transformation
pathway was found to be another important mechanism in Br-DBP formation.
The results of this study highlight the superior potential of our
code for the efficient detection of yet unknown organohalogens (including
organohalogens bearing nonoxygen heteroatoms) in a nontargeted manner
and for the identification of their generation mechanism occurring
during the disinfection process.