Acid hydrolysis of sulphated polysaccharides. Desulphation and the effect on molecular mass

The functionality of sulphated polysaccharides is directly related to the d egree of sulphation of these polymers. Acid hydrolysis is often carried out to study the kinetics of hydrolysis/chain scission of these polymers and t he effect on molecular mass. However, measurement of molecular mass by size -exclusion chromatography (SEC) can be artefactual if the hydrolysis step a lso leads to desulphation of the polymer. A new and sensitive method based on a combination of size-exclusion and ion-repulsion principles has therefo re been developed to enable the rapid measurement of free sulphate (and chl oride 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 polysacchar ides (kappa-, iota-, lambda-carrageenan, dextran sulphate, heparin) during acid (pH 2) hydrolysis at 35 and 55 degrees C. Dextran sulphate was found t o be the most sensitive to desulphation, probably due to its high chain fle xibility. Heparin and the carrageenans were stable to desulphation during t he time period examined here, confirming the suitability and applicability of SEC-based methods for molecular mass determination of these polymers. Th e molecular mass of all but heparin was, however, found to be rapidly lower ed by the (chain scission) hydrolysis. Kinetic parameters for depolymerizat ion have been recovered for these polymers. (C) 1999 Elsevier Science Ltd. All rights reserved.