Fragmentation in the ion transfer optics after differential ion mobility spectrometry produces multiple artifact monomer peaks

Abstract

Differential ion mobility spectrometry (DIMS) can be used to separate isomeric and isobaric ions, which are difficult to distinguish with mass spectrometry alone. Three peaks were observed while performing DIMS-MS for both lithium cationized glucose and lithium cationized levoglucosan. Glucose has a large number of potential structures for its small size. The different peaks could be caused by differences in glucose anomericity, pyranose versus furanose forms, ring conformation, or the lithium cation binding site. However, the bicyclic structure of levoglucosan is more constrained and less likely to result in different structures than glucose.The three peaks for both compounds were found to originate from the monomer, post-DIMS fragmentation of a homodimer, and post-DIMS fragmentation of a heterodimer with a common contaminant, erucamide. This post-DIMS fragmentation occurs in the ion transfer optics and can lead to erroneous conclusions about the peaks in a DIMS spectrum where dimers are present. Dimers are commonly observed when using metal cationization, where over 10% of the glucose and levoglucosan was observed as a lithium cation bound dimer, even at concentrations as low as 0.1 μM.