Laser Electrospray Mass Spectrometry Minimizes Ion Suppression Facilitating Quantitative Mass Spectral Response for Multicomponent Mixtures of Proteins

A comparison of the mass spectral response for myoglobin, cytochrome c, and lysozyme is presented for laser electrospray mass spectrometry (LEMS) and electrospray ionization–mass spectrometry (ESI–MS). Analysis of multicomponent protein solutions using nonresonant femtosecond (fs) laser vaporization with electrospray postionization mass spectrometry exhibited significantly reduced ion suppression effects in comparison with conventional ESI analysis, enabling quantitative measurements over 4 orders of magnitude in concentration. No significant charge reduction was observed in the LEMS experiment while the ESI measurement revealed charge reduction for myoglobin and cytochrome c as a function of increasing protein concentration. Conventional ESI–MS of each analyte from a multicomponent solution reveals that the ion signal detected for myoglobin and cytochrome c reaches a plateau and then begins to decrease with increasing protein concentration preventing quantitative analysis. The ESI mass spectral response for lysozyme from the mixture initially decreased, before increasing, with increasing multicomponent solution concentration.