The baseline resolution of Aldo-monosaccharide enantiomers: Simplified GC-MS analyses using acetal-trifluoroacetyl...

A variety of scientific and technical fields rely on the analysis of monosaccharides (sugars). However, the multiple isomer forms of individual monosaccharides have long hampered their analyses in complex samples: significant chromatographic co-elution often leads to the loss of information on individual compounds. In addition, the chromatographic enantiomer resolution of monosaccharides has of course received less attention than molecular resolution. This would be expected in the case of rare monosaccharides, but enantiomer resolution of erythrose and threose have also received relatively little attention in the literature. Methods that are capable of the simultaneous molecular and enantiomer resolution/identification of suites of monosaccharides in single complicated mixtures are desirable. Here we report the results of attempts to resolve mixtures of the enantiomers of all three‑carbon (3C) to six‑carbon (6C) aldehyde (aldose) monosaccharides as acetal-trifluoroacetyl (acetal-TFA) derivatives by gas chromatography-mass spectrometry (GC-MS); glyceraldehyde (3C) is included as its TFA-only derivative. After a relatively simple derivatization procedure, the analyzed acetals are in the ethyl-, 2-propyl- and 2-butyl-TFA forms. Using chiral (cyclodextrin) and non-chiral (DB-17) GC columns we show that these enantiomer pairs can be baseline resolved - depending on the derivative/GC column combination - and that any single acetal/TFA combination can resolve the majority of enantiomers in a single run. Importantly, ribose and lyxose form only one significant (in abundance) stereoisomer with all derivative combinations while other monosaccharides form a maximum of only two significant stereoisomers: this greatly reduces obfuscation due to crowding on a given chromatogram. We conclude that GC-MS of acetal-TFA derivatives is the best (overall) analytical technique, to date, for the analysis of aldose-monosaccharide enantiomer ratios and reduces chromatogram clutter by favorably restricting the proliferation of monosaccharide isomers.