Organic compounds in saline marine and estuarine sediments 199
8.2.5 Quaternary ammonium compounds
Li and Brownawell et al [48] present a sensitive and robust method of analysis for quaternary ammonium compounds in marine sediments. Methods for extraction, sample
purification, and HPLC-time-of-flight MS analysis were optimised, providing solutions to problems associated with analysis of quaternary ammonium compounds, such
as dialkyldimethlammonium and benzalkonium compounds. The exceptionally high
positive mass defects characteristic of alkylammonium or protonated alkylamine ions
are discussed in this study. No alternative and chemically viable elemental formulas
exists within 25.2 mDa when the number of double band 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 benzalkonium compounds and many
other chemicals, opening up a range of potential applications. The power of utilising a combination of approaches is illustrated with the identification of nontargeted
dialkyldimethylammonium C8:C8 and C8:C10, two widely used biocides previously
unreported in environmental samples. Concentrations of quaternary ammonium in
sewage-impacted estuarine sediments (up to 74 µg/g) were higher than concentrations
of other organic contaminants measured in the same or nearby samples, suggesting
that further study is needed in this field.
8.3 Lacustrine sediments
8.3.1 Aliphatic hydrocarbons
Wakeham et al [49] has discussed the application of synchronous fluorescence spectroscopy in the characterisation of indigenous and petroleum derived hydrocarbons in
lacustrine sediments. The author reports a comparison, using standard oils, of conventional fluorescence emission spectra and spectra produced by synchronously scanning
both excitation and emission monochromators.
8.3.2 Polycyclic aromatic hydrocarbons
Saber et al [21] have reported on the quantitative determination of polyaromatic
hydrocarbons in extracts of lacustrine sediments using high resolution Shpol’skii
spectrofluorimetry at 10 K.
8.3.3 Sterols
Dreier et al [50] determined sterols in lacustrine sediments. Samples of wet lacustrine sediments were heated under anoxic conditions at 150, 175, 200 and 250
◦ C for
5 days; at 175
◦ C with influx of potassium hydroxide and methanol to remove sterols;
and at 175
◦ C for 12, 18, 24 and 48 hours, after which extraction was performed.
Heating the sediment increased the amounts of extractable sterols provided that
the temperature did not exceed 200
◦ C, because degradation became rapid above
8.2.5 Quaternary ammonium compounds
Li and Brownawell et al [48] present a sensitive and robust method of analysis for quaternary ammonium compounds in marine sediments. Methods for extraction, sample
purification, and HPLC-time-of-flight MS analysis were optimised, providing solutions to problems associated with analysis of quaternary ammonium compounds, such
as dialkyldimethlammonium and benzalkonium compounds. The exceptionally high
positive mass defects characteristic of alkylammonium or protonated alkylamine ions
are discussed in this study. No alternative and chemically viable elemental formulas
exists within 25.2 mDa when the number of double band 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 benzalkonium compounds and many
other chemicals, opening up a range of potential applications. The power of utilising a combination of approaches is illustrated with the identification of nontargeted
dialkyldimethylammonium C8:C8 and C8:C10, two widely used biocides previously
unreported in environmental samples. Concentrations of quaternary ammonium in
sewage-impacted estuarine sediments (up to 74 µg/g) were higher than concentrations
of other organic contaminants measured in the same or nearby samples, suggesting
that further study is needed in this field.
8.3 Lacustrine sediments
8.3.1 Aliphatic hydrocarbons
Wakeham et al [49] has discussed the application of synchronous fluorescence spectroscopy in the characterisation of indigenous and petroleum derived hydrocarbons in
lacustrine sediments. The author reports a comparison, using standard oils, of conventional fluorescence emission spectra and spectra produced by synchronously scanning
both excitation and emission monochromators.
8.3.2 Polycyclic aromatic hydrocarbons
Saber et al [21] have reported on the quantitative determination of polyaromatic
hydrocarbons in extracts of lacustrine sediments using high resolution Shpol’skii
spectrofluorimetry at 10 K.
8.3.3 Sterols
Dreier et al [50] determined sterols in lacustrine sediments. Samples of wet lacustrine sediments were heated under anoxic conditions at 150, 175, 200 and 250
◦ C for
5 days; at 175
◦ C with influx of potassium hydroxide and methanol to remove sterols;
and at 175
◦ C for 12, 18, 24 and 48 hours, after which extraction was performed.
Heating the sediment increased the amounts of extractable sterols provided that
the temperature did not exceed 200
◦ C, because degradation became rapid above