CHARACTERIZATION OF HYDROXYETHYL STARCH BY POLYMER ANALYSIS FOR USE AS A PLASMA-VOLUME EXPANDER

Hydroxyethyl starch is currently finding increasing use as a basis material for plasma volume expanders. In clinical applications it is desirable to have a precise knowledge of the steric and chemical structure, as these affect the pharmacokinetics and pharmacology. Characterization involved the determination of the mean molar masses and distribution functions of various hydroxyethyl starches, with molar masses ranging from 40,000 g/mol to 200,000 g/mol and degrees of substitution from 0.38 to 0.64, by means of size exclusion chromatography followed by double detection (MALLS/RI). Hydrodynamic data (Staudinger indices, Huggins constants and equivalent diameters) were determined by viscometric means. The chemical structure of the hydroxyethyl starches were clarified by {H-1}-C-13 NMR spectroscopy. Signal assignment for the {H-1}-C-13 NMR spectra made it possible to carry out an absolute determination of the molar, mean and partial degrees of substitution and the degree of branching. The partial degree of substitution of the carbon atom C-2 was found to constitute between 60 and 80% of the total degree of substitution. This value is significantly larger than the partial degrees of substitution at the atoms C-3 and C-6. which were found to contribute up to approximately 10% and 20% respectively of the total degree of substitution. Degrees of branching ranging from 3.1% to 5.5% were detected.