Molecular weight determination of lignosulfonates by size-exclusion chromatography and multi-angle laser light scattering.

A lignosulfonate sample was fractionated according to the solubility in ethanol-water. The fractions were analysed by aqueous size exclusion chromatography (SEC) combined with in-line multi-angle laser light scattering (MALLS), and by static MALLS. Satisfactory SEC results were obtained with aqueous phosphate buffer containing DMSO and SDS. The refractive index increment (dn/dc) varied from 0.186 to 0.205 ml/g, depending on Mw and the degree of sulfonation. The second viral coefficient (A2) was 7 x 10(-3) ml mol/g2. The weight-average molecular weight (Mw) of the fractions varied from 4600 up to 398 000 g/mol. and the polydispersity (Mw/Mn) varied between 1.3 and 3.5.