A sensitive and robust method of analysis for quaternary ammonium compounds (QACs)
in marine sediments is presented. Methods for extraction, sample purification, and
HPLC-time-of-flight MS analysis were optimized, providing solutions to problems associated
with analysis of QACs, such as dialkyldimethylammonium (DADMAC) and benzalkonium (BAC)
compounds experienced previously. Recognized in this study are the exceptionally high
positive mass defects characteristic of alkylammonium or protonated alkylamine ions.
No alternative and chemically viable elemental formulas exist within 25.2 mDa when
the number of double bond equivalents is low, effectively allowing facile discrimination
of this compound class in complex mixtures. Accurate mass measurements of diagnostic
collision-induced dissociation fragment ions and heavy isotope peaks were obtained
and also seen to be uniquely heavy compared to other elemental formulas. The ability
to resolve masses of alkylamine fragment ions is much greater than for the molecular
ions of BACs and many other chemicals, opening up a range of potential applications.
The power of utilizing a combination of approaches is illustrated with the identification
of nontargeted DADMAC C8:C8 and C8:C10, two widely used biocides previously unreported
in environmental samples. Concentrations of QACs in sewage-impacted estuarine sediments
(up to 74 microg/g) were higher than concentrations of other organic contaminants
measured in the same or nearby samples, suggesting that further study is needed.