The pH Dependence of Product Ion Spectra Obtained from Precursor Ions with the Same Charge Number in ESI of Carbonic Anhydrase 2.

The effect of solvent conditions, including pH, on product ion spectra obtained from precursor ions produced by electrospray ionization (ESI) was examined. Bovine carbonic anhydrase 2 was used as a model protein and the product ions generated by collision induced dissociation of the whole protein were measured under several different solvent conditions (pH 5.0, 3.7, and 0.1% HCOOH (pH 2.6)/MeCN (1/1)). The product ion spectra from precursor ions with the same charge number, the observed m/z values and the relative intensities of the product ions were similar. It therefore appears that the solvent conditions used have no effect on the product ion that is generated. On the other hand, different profiles of the product ion were obtained from precursor ions having different charge numbers. This indicates that the charge number of the precursor ion appears to be a major determinant of the product ion species and its relative intensity in product ion spectra of proteins.