Fragmentation of neutral oligosaccharides using the MALDI LTQ Orbitrap

Abstract Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry is a highly appreciated method in oligosaccharide analysis due to its high sensitivity and ease of use. As underivatized oligosaccharides suffer from low ionization efficiency, derivatization is a widespread tool. However, subsequent sample purification and toxic or otherwise dangerous reagents complicate the oligosaccharides’ analysis. On-target derivatization performed by the matrix 3-aminoquinoline does not require such purification and yields Schiff bases which can be measured in positive and negative ion modes from one single spot. In this article, this simple and convenient method is applied for structural characterization of oligosaccharides using a MALDI LTQ Orbitrap. Information received by the different fragmentation techniques collision-induced dissociation (CID), pulsed-Q dissociation (PQD) and higher energy C-trap dissociation (HCD) are compared. By combining the information received from fragmentation of [M+H] + ions (in positive ion mode) and [M+NO 3 ] − ions (in negative ion mode) of 3-AQ-derivatized species by all three fragmentation techniques, a complete structural characterization in terms of linkage, branching and anomeric configuration of glycosidic bonds of oligosaccharides could be achieved. The analysis of isomeric human milk oligosaccharides derivatized with 3-AQ yielded comprehensive information on the isomers’ structures. Finally, a simple combination of peak lists obtained by the different fragmentation techniques and automatic measurements enhance and facilitate oligosaccharide analysis.