Desorption Electrospray Ionization (DESI)
This proprietary technology was first published by Dr. R. Graham
Cooks’ group in Science (Mass Spectrometry
Sampling Under Ambient Conditions with Desorption Electrospray Ionization,
Science, 2004, 306, 471-473). The diagram below shows a
representation of the component parts of DESI and how an Omni Spray™
ion source would interface with a standard mass spectrometer.
Desorption Electrospray Ionization (DESI) is carried out by directing
pneumatically assisted electrosprayed droplets onto a surface to
be analyzed at atmospheric conditions. Ions are produced from the
sample originally present on the surface. The resulting mass spectra
are similar to normal ESI mass spectra. The contents of the solvent
spray, the gas flow rate, the amount of applied voltage, the spray
angle and the ion uptake angle, as well as the various distances
in aligning the spray, sample and mass spectrometer are all variables
which can be studied to achieve an optimal mass spectrum for a particular
type of sample.
Using DESI, high quality mass spectra have already been obtained
for a wide range of molecules by directly interrogating a diverse
range of surfaces. For example, explosive agents, chemical warfare
simulants, amino acids, peptides, proteins, commercially available
drug molecules, alkaloids, terpenoids and steroids have all been
successfully ionized using DESI. These molecules have been ionized
from a diverse range of surfaces (conducting as well as insulating)
such as plant tissues, human skin, liquid blood, dried blood spots,
urine, as well as from a wide range of inert materials such as polytetrafluoroethylene
(PTFE), nitrile gloves, leather belts, pharmaceutical tablets, and
many more surfaces that we interact with in our everyday lives.
In summary, the benefits of Desorption Electrospray Ionization
include the following:
- DESI is a DIRECT sampling method that requires absolutely no
sample preparation
- DESI operates in the atmosphere under ambient conditions
- DESI is a “sensitive” and “gentle” ionization
method for the analysis or interrogation of all types of surfaces
- DESI produces electrospray-like spectra
- DESI is effective for both organic and biological compounds
- DESI is effective for polar and non-polar molecules
- DESI allows for in situ analysis of biological tissues
and other fragile surfaces
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