Electrospray ionization multicharged ions

Electrospray ionization (ESI) produces a series of multicharged ions that can be transformed into an accurate molecular mass for proteins with masses of tens of thousands. 

Different from the El source, the APCI source contains a heated vaporizer which facilitates rapid desolvation/vaporization of the droplets by a very brief heating period up to 500 °C. Reagent ions obtained from the solvent vapour by a corona discharge ionize the vaporized sample molecules through an ion—molecule reaction. Chemical ionization of sample molecules is very efficient due to the numerous ion—molecule collisions (Figure 16.23). This technique leads to multicharged ions of type (M-F nH)"+ by proton transfer (in the positive mode). Unfortunately this technique is difficult to miniaturize as the required flow rate is higher than that of the electrospray and as such is convenient only for volatile and thermally stable molecules of mass less than 1000 Da. 

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