Desorption electrospray ionization
[4] Therefore, DESI-MS may be applied in a wide variety of sectors including food and drug administration, pharmaceuticals, environmental monitoring, and biotechnology.
DESI has been widely studied since its inception in 2004 by Zoltan Takáts, Justin Wiseman and Bogdan Gologan, in Graham Cooks' group from Purdue University[3] with the goal of looking into methods that didn't require the sample to be inside of a vacuum.
Electrospray ionization with mass spectrometry was reported by Malcolm Dole in 1968,[8] but John Bennett Fenn was awarded a nobel prize in chemistry for the development of ESI-MS in the late 1980s.
One in particular, due to increasing studies into optimization of DESI, is nanospray desorption electrospray ionization (nano-DESI).
[12] The electrospray mist is pneumatically directed at the sample where subsequent splashed droplets carry desorbed, ionized analytes.
After ionization, the ions travel through air into the atmospheric pressure interface which is connected to the mass spectrometer.
[12] High molecular weight molecules, such as proteins and peptides show electrospray like spectra where multiply charged ions are observed.
For the low molecular weight molecules, ionization occurs by charge transfer: an electron or a proton.
These test results indicate that each group of molecules has a different ionization mechanism; described in detail in the Principle of operation section.
The sprayer tip and the surface holder are both attached to a 3D moving stage which allow to select specific values for the four geometric parameters: α, β, d1 and d2.
[15] Another method good for biomolecules is matrix assisted laser desorption electrospray ionization (MALDESI).
In this technique, it utilizes Infrared laser ionization to excite the sample molecules to allow for the desorbed ions to be ready for MS analysis.
A key characteristic of this setup is its ability to separate the distribution of ions generated in DESI prior to mass spectrometry analysis.
Therefore, you can couple a Fourier transform ion cyclotron resonance to DESI, allowing for a higher resolution.
There is negligible dead volume and back pressure that allows for almost real time mass spectrometry detection with a fast elution and purification.
[24] In DESI, there is a high-velocity pneumatically assisted electrospray jet that is continually directed towards the probe surface.
The sample can be dislodged by the incoming spray jet allowing for particles to come off in an ejection cone of analyte containing secondary ion droplets.
They feature multiply charged ions alkali metal adducts and non covalent complexes that originate from the condensed phase of the sample/solvent interaction.
[12] DESI is revealed to have a more gentle ionization condition that leads to a more pronounced tendency for metal adduct formation and a lower specific charging of secondary droplets[citation needed].
