Two‐Dimensional Tandem Mass Spectrometry for Biopolymer Structural Analysis

Biopolymer analysis, including proteomics and glycomics, relies heavily on the use of mass spectrometry for structural elucidation, including sequence determination. Novel methods to improve sample workup, instrument performance, and data analysis continue to be developed to address shortcomings associated with sample preparation, analysis time, data quality, and data interpretation. Here, we present a new method that couples in‐source collision‐induced dissociation (IS‐CID) with two‐dimensional tandem mass spectrometry (2D MS/MS) as a way to simplify proteomics and glycomics workflows while also providing additional insight into analyte structures over traditional MS/MS experiments. Specifically, IS‐CID is employed as a gas‐phase digestion method, i.e., to break down intact full‐length polysaccharide or peptide ions prior to mass analysis. The resulting mixtures of oligomeric ions are analyzed by 2D‐MS/MS, a technique that allows association of product ions with their precursor ions without isolation of the latter. A novel data analysis strategy is introduced to leverage the second dimension of 2D MS/MS spectra, in which stairstep patterns, representing outputs of a molecule's MSn scans, are extracted for structural interconnectivity information on the oligomer. The results demonstrate the potential applicability of 2D MS/MS strategies to the modern omics workflow and structural analysis of various classes of biopolymers. Two‐dimensional tandem mass spectrometry was combined with in‐source fragmentation to visualize fragmentation pathways of biopolymers in a three‐dimensional data domain (Precursor m/z, Product m/z, Intensity). By connecting the experimental points in a stairstep pattern, with the diagonal line where the precursor and product m/z values are equal defining the edge of each stair, the sequence of the biopolymer could be reconstructed.