Chemical-ionization mass spectrometry of methylated hexitol acetates

Abstract

Many of the stereoisomers of methylated hexitol acetates having the same arrangement of O-methyl and O-acetyl groups yield markedly different chemical-ionization (c.i.) mass spectra. For example, 1,4,5-tri- O-acetyl-2,3,6-tri- O-methylglucitol and 1,4,5-tri- O-acetyl-2,3,6-tri- O-methylgalactitol yield clearly distinguishable c.i. mass spectra. The observed differences are reproducible. Hence, chemical-ionization mass spectrometry, when combined with analytical gas chromatography and electron-impact (e.i.) mass spectrometry, is of value in identifying the methylated alditol acetates obtained during methylation analysis of polysaccharides and other complex carbohydrates. The c.i. mass-spectral data that differentiate many of the possible partially methylated glucitol, galactitol, and mannitol acetates are presented. In addition, examples are presented that demonstrate the ability of c.i. mass spectrometry to characterize previously unidentified methylated hexitol acetates.