Measurement of solution properties and molecular weight of hydroxyethyl starches using multi-angle laser light scattering: An interlaboratory comparison

The solution properties of hydroxyethyl starch (HES) vary significantly owing to different measurement parameters adopted and sample structures. Here, a round-robin study was conducted to compare inter-laboratory measurements of solution properties, weight-average molecular weight ( M w ), and molecular weight distribution of four HES candidates covering the low- and medium-molecular-weight range, and 50 commercially available HES 130/0.4 drug samples. Analysis was performed using size exclusion chromatography (SEC) combined with multi-angle laser light scattering (MALLS) and differential refractive index (dRI) detectors. The results indicate that HES molecules in the M w range of 17,000–130,000, with varying degrees of substitution (between 0.4 and 0.8), yielded a refractive index increment ( dn/dc ) value of 0.145 ± 0.003 mL/g (solvent: acetic acid-sodium acetate buffer; wavelength: 658 nm) and that the second virial coefficient ( A 2 ) is correlated with M w . The SEC-MALLS-dRI method for M w determination of HES demonstrated good inter-laboratory reproducibility; however, the study findings suggest that column specifications should be added for HES quality standards. Comparing M w results obtained using common and experimentally corrected dn/dc and A 2 values revealed an influence of dn/dc and A 2 on M w , indicating that the M w acceptance criteria of HES quality standards should be adjusted. • HES solution properties and molecular weight determined by inter-laboratory testing. • Refractive index increment ( dn/dc ) and second virial coefficient ( A 2 ) measured. • We report a reliable dn/dc value for low- and medium-molecular-weight HES. • Molecular weight– A 2 correlation can be used to infer the A 2 value for HES molecules. • M w acceptance criteria of HES quality standards should be adjusted.