Efficient analysis of oligosaccharide-malononitrile derivatives by on-line capillary liquid chromatography/electrospray ionization mass spectrometry

Analyses of oligosaccharide-malononitrile derivatives, which were obtained from the reactions of oligosaccharides with malononitrile under aqueous basic conditions, were conducted by on-line capillary liquid chromatography/electrospray ionization mass spectrometry in negative-ion mode. Among a variety of base catalysts for the derivatization of a oligosaccharide to its malononitrile derivative, sodium hydroxide gave the best result, rather than an amine base, with a rapid and clean conversion. The malononitrile derivative of maltoheptaose was detected with good peak shape at the 20 attomol level by selected ion monitoring. Especially in the analysis of multi-component mixtures of oligosaccharide derivatives, addition of crotonaldehyde to the sample solution for the conversion of excess malononitrile to a non-ionizable and more volatile compound, prior to the injection of sample onto the column, greatly improved the chromatographic resolution and peak symmetry of each oligosaccharide-malononitrile derivative. The order of migration of oligosaccharide-malononitrile derivatives on an aminopropylsilyl column followed the size of the carbohydrate moiety.