SUMMARYTen DEAE (2-(diethy1amino)ethyl) dextran samples were investigated by means of static and dynamic light scattering, viscometry and size-exclusion chromatography (SEC) in combination with on-line small-angle laser light scattering (LALLS) and viscometry (VISC). In dilute solution the behavior of DEAE-dextran was compared with that of unsubstituted dextran and the molecular weight (M) dependences of the radius of gyration R, , hydrodynamic radius R , , intrinsic viscosity [ q ] , second virial coefficient A , and zaverage diffusion coefficient were determined. The relationships for DEAE-dextran dissolved in a 0,8 molar sodium nitrate solution were nearly the same as for dextran dissolved in water with 0,05 wt.-Yo sodium azide and gave the same exponents. The molecular weight dependence of the intrinsic viscosity cannot be described by a Kuhn-Mark-Houwink relationship with a constant exponent. The slope in the plot of log [q] versus IogMdecreases with increasing molecular weight which indicates the occurrence of branching. By means of SEC/LALLS/VISC measurements the molecular weight distributions were determined.The distributions were calculated (1) directly from the light scattering signal, (2) from a calibration line obtained by light scattering data of a DEAE-dextran sample with a broad distribution and (3) from the intrinsic viscosity distribution obtained by the on-line viscosity/refractive index detector in combination with the [q]-M relationship. In order to get the correct molecular-weight dependence of the intrinsic viscosity it is necessary to determine the molecular weight distribution directly by LALLS (technique 1) and to combine this with the appropriate intrinsic viscosity data from the viscometer. Only the third technique, which is an extension of technique 1, gave satisfactory results over the whole molecular weight region observed.

Solutions of hydroxyethyl starch are used as a blood plasma substitute. If their physiological efficiency is to be optimized, they need to be accurately characterized in terms of their molecular weight and its distribution. The absolute determination of molecular weight and molecular weight distribution by means of light scattering require a knowledge of the refractive index increment. Although numerous investigations of the refractive index increment of hydroxyethyl starch have already been published, the results vary significantly due to the use of different samples and the choice of different measuring parameters. There was therefore an urgent need to examine the extent to which the refractive index increment depends on molecular parameters, the experimental method used and the type of processing. Here it was found that different sample preparations result in different contents of solid matter, so that an exact determination of the quantity is required. Hydroxyethyl starches in the molecular weight range of about Mw = 200.000 g/mol and varying degrees of substitution between DS 0.38 and 0.50 which are regarded as optimal for clinical use give a refractive index increment of dn/dc633nm = 0.146 = 0.005 cm3/g (solvent: H2O/0.02% NaN3; T = 25°C).

Blood plasma substitutes, such as dextran and hydroxyethyl starch, cause an expansion of the liquid volume in blood vessels due to their high colloid‐osmotic pressure and water‐binding potential, and are therefore applied clinically as so‐called plasma expanders for rapidly increasing the liquid volume. This potentially life‐saving effect only applies while the plasma substitute is present in the bloodstream. For this reason knowledge of the retention time is of great importance. As the retention time is directly related to the molecular weight distribution of polydisperse hydrocolloids, an estimation of the parameters of this distribution is therefore of crucial significance in the quality control of plasma expanders. Besides absolute methods (e.g. GPC/LALLS), there is special interest in GPC as a relative method with calibration against narrow molecular weight standards. This is because of its wide distribution, the speed at which it can be carried out, and the low expenditure on apparatus. Furthermore, there are advantages if commonly accepted pharmacopoeial methods can be performed in a manner that allows the results to be compared easily. In order to implement the molecular weight determination method in Pharmacopoeia Nordica's (Ph.Nord, or Svensk Läkemedelsstandard “SLS”) dextran monograph, a suitable software for VAX computers was developed at the Max Planck Institut für Kohlenforschung in Mülheim/Ruhr.