Interpreting Mass Spectra of Multiply Charged Ions

Abstract

We describe two algorithms that extract molecular mass Information from spectra showing sequences of peaks due to Ions with varying numbers of charges. The first, called here the “averaging algorithm”, unambiguously assigns charge numbers to the ions associated with the m/z value for each peak in the sequence and then averages the resulting values of M to give a best estimate of the molecular mass. The second, Identified as the “deconvolutIon algorithm”, mathematically transforms a spectrum of several peaks for multiply charged ions into one peak corresponding to a singly charged Ion. The procedures can be readily implemented with a personal computer and are here applied to representative spectra of small proteins generated by electrospray mass spectrometry. These algorithms are now routinely used in our laboratory for the Interpretation of such spectra. They both are fast and convenient, discriminate against background, and take advantage of much of the information contained in a sequence of peaks. Achievable accuracy and sources of error are discussed. © 1989, American Chemical Society. All rights reserved.