Parent Ion Scans of Large Molecules

Abstract

The utility of parent ion scans for the selective detection of small molecules which yield indicative fragments in tandem mass spectrometry is well recognized. This work established the feasibility of parent (or precursor) ion experiments with large molecules such as proteins and oligonucleotides. Tandem mass spectrometry of proteins yields substantial and specific immonium ion fragmentation and fragments characteristic of post-translational modifications. Phosphoproteins are specifically detected by parent ion scans of the phospho group (PO3-) in the negative ion mode. The same ion allows mass measurements of oligonucleotides with improved signal-to-noise ratio. Scans for the parents of the oxonium ion of hexosamine distinguish glycoproteins from other proteins in mixtures. Parent ion scans of intact proteins is a novel concept which may find applications in the determination of post-translational modifications, in protein charting and in the study of the fragmentation behavior of large molecules. © 1997 by John Wiley & Sons, Ltd.