Electrospray analysis of proteins: A comparison of positive‐ion and negative‐ion mass spectra at high and low pH

Cationic and anionic electrospray mass spectra were measured for equine myoglobin, lactalbumin and hen egg white lysozyme from acidic and basic solutions. Both positive and negative ions were detected from all solutions in which the proteins were soluble. This was observed in both nebulization‐assisted and thermally assisted electrospray. As in other studies, the distribution of the charge states reflected functional groups in the proteins, and also folding or extension of the protein.