Fundamentals of Biomolecule Analysis by Electrospray Ionization Mass Spectrometry. An Instrumental Analysis Laboratory Experiment

This article describes an undergraduate instrumental analysis laboratory experiment dealing with fundamentals of electrospray ionization mass spectrometry (ESI–MS). Several important aspects of applications of ESI–MS for analysis of biomolecules are addressed. First, the formation of multiply charged ions and deconvolution of such ESI spectra to yield the molecular mass of the analyte is discussed. Second, the effects of isotopic contribution (mostly of 13C) are observed experimentally and verified by calculations. Last, the resolution of a mass spectrometer is probed as the ability to resolve individual peaks in isotopic clusters. Although the experiment is described for quadrupole ion trap mass spectrometers (two major manufacturers’ machines are tested here), it can be applied to virtually any ESI–MS instruments with minor modifications.