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.