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| Figure
9 - click on figure to enlarge |
|
Tests involving sequential
flow injections of microextracts of Vineyard Sound surface
water demonstrated a linear mass spectrometer response for
both total ion current and specific ion fragmentation pathways
for target surfactants in the water. Figure 9 shows a 25-sample
time series in which quantitation of a model surfactant, a
small surface-active oligopeptide spiked into the seawater,
was carried out using the automated macrotrap extraction system
and ITMS with electrospray ionization (ESI) with virtually
no chemical noise. The sample size was modulated in a sawtooth
pattern to simulate varying surface microlayer concentrations.
The mass spectrometer response is quite linear for both the
total ion current and for specific detection of the peptide
using two stages of MS (MSxMS) to follow loss of water (-
18 amu) from the sodium-cationized molecular ion. Each peak
in the mass chromatograms represents one flow-injected extract,
such that the envelope of peak intensities (or peak areas)
corresponds to the concentration ‘profile’ and
could be used to determine the original concentration of the
peptide in the microlayer. |
