Electrospray ionization charge reduction

We have previously considered the mechanism of electrospray ionization in terms of the charging of droplets containing analyte and the formation of ions as the charge density on the surface of the droplet increases as desolvation progresses. The electrospray system can also be considered as an electrochemical cell in which, in positive-ion mode, an oxidation reaction occurs at the capillary tip and a reduction reaction at the counter electrode (the opposite occurs during the production of negative ions). This allows us to obtain electrospray spectra from some analytes which are not ionized in solution and would otherwise not be amenable to study. In general terms, the compounds that may be studied are therefore as follows ... 

Muddknan, D.C. Cheng, X.H. Udseth, H.R. Smith, R.D. Charge-state reduction with improved signal intensity of oligonucleotides in electrospray ionization mass spectrometry. J. Am. Soc. Mass Spectrom. 1996, 7, 697-706. 

Cheng, X. Gale, D. C. Udseth, H. R. Smith, R. D. Charge state reduction of oligonucleotide negative ions from electrospray ionization. Anal. Chem. 1995, 67, 586-593. 

A characteristic feature of ESMS is the detection of multiply charged analytes. Macromolecules, such as proteins have multiple sites where protonation or deprotonation (the two most common charge inducing mechanisms in electrospray—other routes to charge induction include, ionization through adduct formation, through gas-phase reactions, and through electrochemical oxidation or reduction) occur. These are desorbed effectively in ESMS and... 

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