Enhancement of detection for partially methylated alditol acetates by chemical ionization mass spectrometry

Abstract

Chemical ionization (methane) mass spectrometry can be used to greatly enhance the sensitivity of detection of partially methylated alditol acetates of neutral and amino sugars by removing background from gas chromatograms. Limited mass chromatograms can be constructed by plotting the intensity of (MH-60) + ions for neutral sugar derivatives and (MH) − ions for amino sugar derivatives at each mass spectrometric scan number. Each substitution of a methyl with an acetyl group (signifying a glycosidically substituted sugar) increases the mass of the partially methylated alditol acetate by 28 daltons. Therefore, each set of derivatives of a certain substitution number can be plotted by a single ion of high intensity. These can be plotted individually, showing mass chromatograms that can depict terminal, mono-, di-, or higher substituted derivatives. More useful is a composite multiple mass chromatogram giving a complete profile of all possible sugar derivatives in the sample, but with greatly enhanced signal-to-noise ratio. Starting with a weighed amount of known standard and diluting to known concentration of the final derivative, we can detect usable peaks from as little as 100 pg per peak, with 1 to 10 ng suitable for routine analysis. Starting with an unknown sample of saccharide and preparing the partially methylated alditol acetates requires more material, due to losses during preparative steps. Useful information can be gained from 5 to 20 μg of oligosaccharide.