Gosch, C., Haase, T., Wolf, B. A., Kulicke, W.-M.

"Characterization of Hydroxyethyl Starch separated by means of Continuous Polymer Fractionation using combined methods of SEC/MALLS/DRI to determine molar mass distribution and particle size"

Abstract: Hydroxyethyl starch (HES) is increasingly being used as an ingredient of plasma expanders because it exhibits the least severe side effects in comparison with other agents like dextrans and gelatines. In addition to the chemical structure it is also important to have a knowledge of the molar mass and particularly the absolute molar mass distribution, as the latter affects the pharmokinetics such as retention time, volume effect, metabolic reactivity and anaphylactoid reactions. The high molar mass weight fraction is suspected to induce life-threatening anaphylactoid reactions. Only an absolute method using a combination of fractionation such as size exclusion chromatography (SEC) with multi angle laser light scattering (MALLS) and concentration detection as differential refractive index (DRI) enables the molar mass distribution to be determined absolutely.
The use of continuous polymer fractionation (CPF) enables the initial polymer to be separated into fractions of different molar masses, which makes it possible to obtain tailor-made hydroxyethyl starch fractions depending on the application. Two samples of HES (HES A and HES B) were fractionated by means of CPF. By SEC/MALLS/DRI measurements we showed that CPF is able to remove the low-molar-mass components and to adjust the samples to various desired molar masses with lower polydispersities than the original samples. In terms of the weight-average mean molar mass MW, the sol fractions have smaller molar masses than the starting sample, whilst the gel fractions have higher molar masses. Furthermore the radius of gyration RG could be determined for the initial sample HES B and its fractions. However, no general RG-MW relationship could be established by the HES samples fractionated using CPF. MW and MW/Mn of the six fractions obtained from HES A with MW = 161,000 g/mol and MW/Mn = 4.7ranged from 19,000 to 362,000 g/mol with MW/Mn from 1.8 to 5.1. The molar masses of the four fractions obtained from HES B with MW = 460,000 g/mol and MW/Mn = 6.0 were between 18,000 and 680,000 g/mol with MW/Mn from 1.7 to 4.8 or between 202,000 and 1,005,000 g/mol with MW/Mn from 2.7 to 4.7 depending on fractionation strategy.

Carbohydrate Research 2001, 9, 54, 375-384.

preprint number: 222