MECHANISM OF PRODUCTION OF IONS IN ELECTROSPRAY MASS-SPECTROMETRY

A mechanism for the production of multiply charged molecular ion speci es in electrospray mass spectrometry (ES-MS) is still required. A conc ise discussion of a recently published ionic solution equilibrium mode l offering a partial mechanism is presented. That publication proposed that the ion abundance-charge profile could be fitted by one or a ser ies of superimposed Gaussian functions, in accord with a solution equi librium model. It is shown that indeed a simulated mass spectrum based on a solution model can compare well with the observed spectrum. Howe ver, some new and recently published experimental evidence is presente d which shows that the ES mass spectra of many proteins give rise to m ultiply charged molecular ions which carry higher charges than those c alculated by the model. Further, the ion abundance-charge profile is v ery sensitive to some experimental parameters, e.g. cone voltage; it d oes not necessarily reflect the solution or gaseous ion populations in the mass spectrometer source. Therefore, the concept that gaseous mul ti-charged ions originate from equivalently charged solvated ions in e lectrically neutral solution must be treated with caution.