We have recently introduced plasma-assisted reaction
chemical ionization mass spectrometry (PARCI-MS) for elemental
analysis of halogens in organic compounds. Here, we utilize gas
chromatography (GC) coupled to PARCI-MS to investigate the
mechanism of Br− ion generation from organobromines and to
evaluate analytical performance of PARCI for organobromine analysis.
Bromine atoms in compounds eluting from GC are converted to HBr
in a low-pressure microwave induced helium plasma with trace
amounts of hydrogen added as a reaction gas. Ionization is achieved by
introducing nitrogen into the afterglow region of the plasma, liberating
electrons via penning ionization and leading to formation of negative
ions. We demonstrate that N2 largely affects the ionization process,
whereas H2 affects both the ionization process and in-plasma reactions.
Our investigations also suggest that dissociative electron capture is the main ionization route for formation of Br− ions.
Importantly, GC-PARCI-MS shows a uniform response factor for bromine across brominated compounds of drastically different
chemical structures, confirming PARCI’s ability to quantify organobromines in the absence of compound-specific standards. Over
3 orders of magnitude linear dynamic range is demonstrated for bromine quantification. We report a detection limit of 29 fg of
bromine on-column, ∼4-fold better than inductively coupled plasma-MS.