COMPARISON OF DIFFERENT METHODS FOR DETERMINATION OF MOLECULAR-WEIGHT AND MOLECULAR-WEIGHT DISTRIBUTION OF ALGINATES

The scope of the present work was to assess and compare different methods to determine molecular weight (MW) averages and molecular weight distributions (MWD) of two samples of sodium alginate of different composition. Weight average (MBAR(w)) and number average (MBAR(n)) molecular weights were determined by totally integrated laser light scattering (LLS), both at wide angles (WA) and at a low angle (LA), and membrane osmometry, respectively. The two alginates were fractionated by preparative and analytical size exclusion chromatography. Absolute molecular weight distribution curves were obtained from SEC, using an on-line LA-LLS detector coupled with an RI concentration detector. Relative MWD curves were determined from 'universal' calibration of the SEC data. MBAR(w), MBAR(v), and MBAR(n) were calculated from the 'universal' calibration curve and [eta]j values of the fractions. Good correlation between molecular weight averages obtained from the different methods was observed. Mark-Houwink-Sakurada parameters, a and K, for the two different alginate samples have been determined.