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My research focuses on improving
mass spectrometry instrumentation for the analysis
and quantification of large biomolecules, including
whole proteins. Using mass spectrometry, it
is easier to analyze small molecules than large
molecules. One reason for this bias toward smaller
molecules is sample introduction. In order for
samples to be analyzed by mass spectrometry,
the sample needs to be in the gas phase and
ionized. It is much easier to introduce smaller
molecules into the gas phase using traditional
methods, because large molecules tend to decay
rather than evaporate. Methods such as electrospray
ionization (ESI) and matrix assisted laser desorption/
ionization (MALDI) are capable of introducing
large molecules into the gas phase, however,
these methods have their own disadvantages.
With electrospray ionization, for example, each
species can have many different charge states
leading to complex spectra from which quantitative
data is difficult to extract.
Another reason
for mass spectrometer bias toward small molecules
involves current detection systems, which show
better response and sensitivity with small molecules.
This small molecule bias results in the need
to digest large proteins into small peptides
in order for the sample to be analyzed. Digesting
proteins into small peptides increases the complexity
of the resulting spectra.
In order to improve
mass spectrometers for the analysis of biomolecules,
it is necessary to improve ionization methods
and detectors. New ionization techniques need
to be developed that provide uniform ionization
efficiencies for all peptides and proteins,
regardless of sequence or functional groups.
Furthermore, it is desirable for ionization
techniques to yield molecules in a single charge
state, eliminating the complexity and difficulty
of extracting quantification data from spectra
of molecules in multiple charge states. We are
developing an ionization technique that creates
neutral gas phase molecules and then allows
them to undergo controlled gas phase proton
transfer reactions. These reactions would result
in molecules having a single positive charge
state. By using this method under the proper
conditions, ionization efficiency will only
be dependent upon molecular weight, which can
be accounted for by using physical collision
models or calibration curves with known masses.
In addition, by improving detector response
to high molecular weight molecules, it will
be possible to analyze whole proteins without
the need for digestion. The new detectors developed
should also have high sensitivity with low noise
levels, a large dynamic range, fast response
times, fast recovery times, and a large active
area.
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