  H-abstraction reactions occurring on electron ionization mass spectrometry
(EI-MS) are a long-standing and crucial topic in MS research. Yet some critical
relevant mechanisms are controversial and ambiguous, and information about the
EI-induced H-abstraction reactions of halogenated organic compounds (HOCs) is
completely in the dark. This study provides a systematic investigation of
H-abstraction reactions of HOCs taking place on EI source using
13C6-hexachlorobenzene (13C6-HCB) and 13C6-hexabromobenzene (13C6-HBB) as
exemplary compounds by gas chromatography high resolution mass spectrometry
(GC-HRMS). The H-abstraction efficiencies were evaluated with the MS signal
intensity ratios of ions with H-abstraction relative to the corresponding
original ions (without H-abstraction). Ion source temperatures, EI energies and
numbers of heavy isotope atoms (37Cl or 81Br) of isotopologues were
investigated in terms of their effects on the H-abstraction efficiencies. The
H-abstraction efficiencies of individual isotopologues generally decreased from
the first to the last isotopologues of respective ions, and those of individual
ions were different from each other, with the highest values of 0.017 and 0.444
for 13C6-HCB and 13C6-HBB, respectively. The overall H-abstraction efficiencies
involving all measured ions of 13C6-HCB and 13C6-HBB were 0.004 and 0.128,
respectively. EI energies and emission currents could impact the H-abstraction
efficiencies. The H-abstraction reactions were inferred to belong to
ion-molecule reactions. Some strategies were proposed for eliminating or
alleviating the interference triggered by the H-abstraction reactions on EI-MS
in identification of halogenated organic pollutants (HOPs). Our findings
provide a better understanding for the EI-induced H-abstraction reactions of
HOCs, and may benefit identification of HOPs in environmental analysis,
especially for novel HOPs.
