Quantitative determination of chitosans by ninhydrin

The functionality of sulphated polysaccharides is directly related to the degree of sulphation of these polymers. Acid hydrolysis is often carried out to study the kinetics of hydrolysis/chain scission of these polymers and the effect on molecular mass. However, measurement of molecular mass by size-exclusion chromatography (SEC) can be artefactual if the hydrolysis step also leads to desulphation of the polymer. A new and sensitive method based on a combination of size-exclusion and ion-repulsion principles has therefore been developed to enable the rapid measurement of free sulphate (and chloride if needed) levels in polymer solutions without any sample separation/preparation step. This and an SEC¯refractive index method have been used to follow the desulphation and depolymerization of five sulphated polysaccharides (kappa-, iota-, lambda-carrageenan, dextran sulphate, heparin) during acid (pH 2) hydrolysis at 35 and 55°C. Dextran sulphate was found to be the most sensitive to desulphation, probably due to its high chain flexibility. Heparin and the carrageenans were stable to desulphation during the time period examined here, confirming the suitability and applicability of SEC-based methods for molecular mass determination of these polymers. The molecular mass of all but heparin was, however, found to be rapidly lowered by the (chain scission) hydrolysis. Kinetic parameters for depolymerization have been recovered for these polymers.