Indirect fluorescence detection of amino sugars with the use of copper complexes of tryptophan and its analogues following high-performance liquid chromatographic separation

A simple, indirect fluorescence detection method has been developed for detecting specific mono-amino sugars (D-glucosamine, D-galactosamine, D-mannosamine) following chromatographic separation. The eluting amino sugars release L-tryptophan (L-Trp) from a copper-tryptophan complex which is introduced postcolumn. Analyte detection is based on measuring the increase in L-Trp fluorescence, which is quenched when complexed with copper. Two tryptophan analogues, 5-hydroxy-L-tryptophan (5-HTP) and DL-5-methoxytryptophan (5-MTP), were also evaluated as postcolumn reagents. 5-MTP was found to be a suitable alternative to L-Trp for the detection of these mono-amino sugars. Detection limits for D-glucosamine, D-galactosamine, and D-mannosamine are in the range of 0.15-0.30 nmol injected.