Electrospray ionization
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Electrospray ionization is a technique used in mass spectrometry to overcome the propensity of macromolecules to fragment. The invention of electrospray ionization was rewarded with the attribution of the Nobel Prize in Chemistry to John Fenn in 2002.
In electrospray ionization a liquid is pushed through a very small charged metal capillary by a carrier gas. The liquid contains the substance which is to be studied, the analyte, as well as a large amount of solvent, which is usually much more volatile than the analyte. The charge contained in the capillary transfers to the liquid which charges the analyte molecule. As like charges repel, the liquid pushes itself out of the capillary and forms a mist or an aerosol of small droplets about 10um across, to increase the distance between the similarly charged molecules. A neutral carrier gas is sometimes used to evaporate the neutral solvent in the small droplets, this in turn brings the charged analyte molecules closer together. The proximity of the molecules becomes unstable, however, and as the similarly charges molecules come closer together, the droplets once again explode. This process repeats itself until the analyte is free of solvent and is a lone ion. The lone ion will then continue along to a mass analyzer.
Links
- Electrospray Ionization from Cambridge University (http://www-methods.ch.cam.ac.uk/meth/ms/theory/esi.html)