N-phthaloyl chitosan is able to form cholesteric liquid crystalline ohase in concentrated solutions of some organic solvents

including DMF

DMSO

DMAc and pyridine．Circular dichroism was applied to investigate the change of handedness for the above four systems．CD spectra suggested two kinds of absorption peaks when the concentration was highelf than a critical concentration for forming liquid crystalline phase One is a sharp peak at 330 nm

the other is a broad peak with a maximum at about 400～450 nm．However only sharp peak at 330 nm was observed for isotmpic solutions．The sharp peak was induced by the helical conformation of molecular chains

and the broad peak was induced by the cholesterie helices of liquid crystal．Therefore the determination of the critical concentration for N-phthaloyl chitosan solutions by monitoring the very beginning of the appearance of the broad Deak is feasible The critical concentrations measured by CD were 1 wt％ lower than those measured by polarized optical microscopy (POM) for all four solvents used．It means

as a method to measure the critical concentration

CD is more sensitive than POM．Two different ways of sample tilt were used in CD messurements to prove that the linear dichroism and birefringance had no effect on CD signal of cholesteric helices of the liquid crystal．