2.3. Sample hydrolysis and derivatization
Samples containing either 50 mg chitosan or glucosamine were
weighed into thick-walled glass digestion tubes, 2 mL of 1% acetic
acid solution was added, and the mixture vortexed until it formed
a consistent gel. Chitosan was hydrolyzed following the addition
of 10 mL concentrated HCl (8, 10, or 12 M) and heat (90 or 105 ◦C).
After a designated period of hydrolysis (for kinetic studies, the samples
were taken at 30 min intervals), the digestion mixture was
cooled to room temperature and subsampled (1 mL) into a mixture
of sodium borate (3.8 g) and DI water (30 mL). The pH was adjusted
to 7.00 with 10 M HCl and the solution volume adjusted to 50 mL
using 0.2 M borate buffer, pH 7.0.
Glucosamine in the hydrolysate was derivatized by mixing 1 mL
of the dilute neutralized solution with 1 mL of 10 mg/mL Fmoc-OSu
in acetonitrile and the reaction was allowed to progress to completion
at ambient temperature for at least 4 h without agitation.
After derivatization, the sample was diluted with 3 mL HPLC mobile
phase (0.05% TFA/ACN, 1:1 (v/v)) for analysis.