The monosaccharides comprise a number of isomers and homologues having very similar structures, basically composed of hydroxymethyl or hydroxymethine groups linked to each other. In reducing monosaccharides the hemiacetal group is at the reducing ends in addition to these polyhydroxylated basal structures. There are other series of monosaccharides with the ketal or carboxyl group instead of or in addition to the hemiacetal group. Substitution of the hydroxyl group by the hydrogen atom or the amino group produces the deoxy sugar or the amino sugar, respectively. All these functional groups give monosaccharides hydrophilic properties. With the exception of monosaccharide residues containing a carboxyl group, detection of these compounds following chromatographic and electrophoretic separation is rendered difficult owing to their inherent lack of chromophores in the ultraviolet (UV) and visible spectrum regions. Obviously, oligosaccharides and polysaccharides composed of these monosaccharide units have a similar shortcoming with respect to their detection.
