Figure 3.

Use of limited charge reduction for identification of cross-linked transferrin oligomers in native MS. A high degree of structural heterogeneity causes ion peaks at different charge states to overlap (black trace). Mass selection of narrow ionic populations followed by their charge reduction via a gas-phase electron transfer from an anion to the protein polycation generates resolved charge ladders (blue and red) that can be used to identify all protein species in the sample (transferrin dimers and trimers, respectively).