Correlation of SEC/MALLS with ultracentrifuge and viscometric data for chitosans

Attempts have been made to correlate estimates of molecular weight for a group of cationic polysaccharides known as chitosans between the highly popular technique of size-exclusion chromatography coupled to multi-angle laser light scattering, "SEC-MALLS", and the less convenient but more established technique of sedimentation equilibrium in the analytical ultracentrifuge. Four pharmaceutical grade chitosans of various molecular weights and degrees of acetylation (4-30%) were chosen. Better correlation than previous was achieved, although some batch variability was observed. Despite the broad spectrum in degree of acetylation, a logsdegrees(20,w) versus logM(w) scaling plot appeared to fit a straight line with power-law exponent b=0.25+/-0.04, i.e. between the limits of rod (0.15) and coil (0.4-0.5), although this may be the average of a lower b value at low M-w and higher b at high M-w. With regard to viscosity, a log[eta] versus logM(w) scaling plot appeared to also fit a straight line with power-law exponent a=0.96+/-0.10, again between the coil (0.5-0.7) and rod (1.8) limits.