CHARACTERIZATION OF CHITOSANS VIA COUPLED SIZE-EXCLUSION CHROMATOGRAPHY AND MULTIPLE-ANGLE LASER LIGHT-SCATTERING TECHNIQUE

Chitosan [(1 --> 4)-2-amino-2-deoxy-beta-D-glucan], a cationic biopolymer, was obtained by deacetylation of chitin samples from various sources. Nine chitosan samples differing in their degree of acetylation and molecular weight were used in this study. They were characterized by size-exclusion chromatography (SEC) coupled to a multiple-angle laser light-scattering (MALLS) photometer. The results show that accurate, reliable, and reproducible molecular weight and radius of gyration data are obtained by using SEC-MALLS. These samples were also characterized by a conventional secondary calibration technique. The molecular weights obtained by secondary calibration were found to be 2-3 times higher than those obtained using SEC-MALLS. The dissimilarity between the chitosan samples and polymer standards employed for calibration were presumed to be responsible for overestimation of the molecular weights. Therefore, we conclude that the unavailability of chitosan polymer standards underscores the need of an absolute molecular-weight determination technique, such as SEC-MALLS. This technique can be used for establishing structure-function relationships of chitosans and as a quality control tool for monitoring bulk production of chitosans.