Improved analysis of oligosaccharides for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using aminopyrazine as a derivatization reagent and a co-matrix

Analysis of oligosaccharides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is often limited by their low ionization efficiency and inadequate fragmentation information. Derivatizations of oligosaccharides to enhance their ionization in MS are widely used, but most of these methods require tedious cleanup steps that may cause sample losses. Here, aminopyrazine is developed as the derivatization reagent as well as the co-matrix to improve the detection of oligosaccharides by MALDI-TOF MS. The purification step is eliminated because aminopyrazine acts as the co-matrix after nonreductive amination derivatization of oligosaccharides. Under optimal conditions, nearly complete derivatization (>95%) is obtained and S/N ratios of oligosaccharide are increased by about 2-6 fold with good signal reproducibility (RSD = 7%). Improved analysis of glycans is also achieved without any prior separation from the mixture of glycans and deglycosylated tryptic digest of glycoproteins. In addition, enhancement of MS/MS fragmentation of derivatized oligosaccharides facilitates their structural elucidation. The proposed derivatization technique is successfully applied to the profiling of N-linked glycans derived from chicken ovalbumin.