electrospray ionisation(redirected from ESI)
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electrospray ionisationA process in mass spectrometry in which a solution containing the molecules of interest is pumped through a metal capillary tube maintained at a high potential. The solution is sprayed from the tube into a chamber held at ground potential and open to atmospheric pressure.
The sample solution spray’s droplets carry a charge induced by the needle potential; the droplets in the mist become progressively smaller as neutral solvent molecules evaporate. The charge is maintained on the droplets’ surfaces, eventually causing an instability that results in the expulsion of solvent-less, highly charged ions of the dissolved sample molecules. Multiple protonation forms highly charged sample molecules of the form (M nH)n.