The Partial Molar Volumes of Chondroitinsulfate A with Various Counterions

Abstract

Densities of, aqucous solutions of chondroitinsulfate A (ChS-A) were measured on a precision densitometer at 298.15, 310.15 and 323.15 K in the concentration ranging from ca.0.005 to 0.11 monomol/dm³. The counterions used in this work were Li, Na, K, NH₄, (CH₃)₄ N, Ca, Ba and Al.
The apparent molar volumes, Φ, calculated from the above results were extrapolated to zero concentration to give the partial molar volumes at infinite dilution, The values were found to be nonadditive, which could he explained on the basis of counterion site binding. From the analysis of the fraction of counterion site binding, β_SD, was found to he ca.0.30 for alkali metal salts, ca.0.43 for alkali earth metal salts and 0.53 for Al salt. The β_SD value was compared with the fraction of ion binding, (1-Φ), derived from the molal osmotic coefficient, Φ. The former was found to he nearly equal to half the latter. From the discussion of β_SD for alkali metal salts, it was tentatively proposed that the counterion site binding mainly occurred at the carboxyl groups.