Chitosan (2 g) was dissolved in dilute acetic acid and dried under vacuum until the content became a gelatinous paste.
100 mL of concentrated HCl (37%) was added and the suspension heated for 30 min at 72◦C under stirring. The reaction was stopped by immersion in an ice bath. Most of the solvent and HCl was evaporated under vacuum; the residue was then resuspended in water and the solution evaporated,those last two operations being repeated twice. The residue was finally dissolved in water and the solution brought to pH 6.5 by addition of concentrated 10 M NaOH.