User:Nmanicke/Desorption elecrospray ionization

=Desorption Electrospray Ionization= Desorption electrospray ionization (DESI) is an ionization technique used to create gas phase ions for analysis by mass spectrometry (MS). First described in 2004, DESI is the first ionization method, and remains one of the only, to allow ambient sampling for MS analysis.

How it works
DESI is an ambient ionization method in which a stream of charged microdroplets is directed at a surface in the open environment. Analyte molecules on the surface are then desorbed due to electrostatic, pneumatic, or chemical processes and collected by the mass spectrometer at an atmospheric pressure interface (API). This method shares a number of essential features with electrospray ionization, in that both create charged droplets by spraying a solution from an electrically charged capillary, both can generate positive or negative ions depending on the potential bias applied to the spray tip, and the charged analyte molecules from both methods can be loaded into the mass spectrometer using the same API. The key difference between the two ionization methods involves the phase of the sample. In ESI, the sample must be dissolved in the spray solvent. Samples analyzed by DESI can be solid, liquid, or absorbed gases. In DESI sample analysis, the sample is typically placed on a movable stage in the open air, and an ESI-style spray with a potential of about 3 kV is directed at the surface. The distances between the sample, the capillary tip and the API, along with the incident spray angle and collection angle, can all be varied to optimize ion signal.

Applications
Ths most striking feature of DESI is that sample analysis occurs in the open environment.