Ascertaining hydrogen-abstraction reaction efficiencies of halogenated organic compounds on electron ionization mass spectrometry

TL;DR

This study systematically investigates hydrogen-abstraction reactions of halogenated organic compounds in electron ionization mass spectrometry, revealing efficiencies, influencing factors, and implications for environmental pollutant identification.

Contribution

It provides the first detailed analysis of EI-induced H-abstraction reactions of halogenated organic compounds using isotopologue data and evaluates factors affecting reaction efficiencies.

Findings

H-abstraction efficiencies vary among isotopologues and compounds.

Ion source temperature and energy influence H-abstraction efficiency.

Strategies are proposed to reduce interference in pollutant identification.

Abstract

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.