A novel, ultrasensitive approach for quantitative carbohydrate composition and linkage analysis using LC-ESI ion trap tandem mass spectrometry

Glycan identification and characterisation is essential to correlate glycoconjugate structure to biological function. The structural assignment of carbohydrates is often based on MS composition analyses and knowledge on well-studied glycosylation pathways. Nevertheless, many monosaccharide building blocks are indistinguishable by mass alone and detailed linkage information is also not easily obtained by MS/MS analyses, in particular when organisms are studied where the glycosylation pathways are less well defined. Here, we present a novel, simple and sensitive method using Reversed Phase (RP) - Liquid Chromatography Electrospray ionisation tandem mass spectrometry (LC-ESI-MS/MS) for unambiguous identification and linkage determination of monosaccharides including N-acetylneuraminic acids. Sequential permethylation and reductive amination steps are employed prior and after acid hydrolysis to enable separation and differentiation of the various monosaccharides and their respective linkage positions. The well-established, monosaccharide specific methylation patterns allowed for the identification of the various derivatised monosaccharide alditols based on their retention time and tandem mass spectrometry fingerprint. Absolute quantitation can also be accomplished by including a set of internal standards, thus simultaneously providing qualitative and quantitative information on the monosaccharide residues present.