The Assignment of Charge States in Complex Electrospray Mass Spectra

In the present paper a new approach to the assignment of charge states in complex electrospray ionisation (ESI) mass spectra, entitled the MassProb procedure, is presented and discussed. This new procedure is a multisolution method in which probabilities for all possible solutions within prespecified ranges of mass and charge are assessed and the most probable in the mass range is selected. In each successive step, probabilities are recalculated and the most probable charge state assignment is selected. Following the assignment of charge states to the ion peaks, the molecular masses of the components of the mixture are calculated in the normal manner.

The paper compares the results obtained using the MassProb procedure to determine the molecular masses (M _r s) of the components of three complex mixtures of proteins and glycoproteins with those found using two commercially available procedures, namely MaxEnt and VGtrans. The overall conclusion reached from this comparative study is that a fully comprehensive solution has yet to be found to the problem of disentangling the raw complex ESI mass spectra of differing quality produced by such multicomponent mixtures. The paper is concluded with a brief survey of the approaches to the problem adopted by others in order to place in context the characteristic features of the MassProb procedure.