VOLTAMMETRIC STUDIES OF COUNTERION TRANSPORT IN SOLUTIONS OF CHONDROITIN SULFATE

The transport of hydrogen counterions was studied in solutions of a li near polyelectrolyte, chondroitin sulfate, CS, by voltammetric measure ments at a platinum disk microelectrode. The use of microelectrodes en ables voltammetry of the counterion in solutions with little or no sup porting electrolyte over a wide range of polyelectrolyte concentration s. The voltammetric interactions of counterions with polyions diminish transport-limited current for reduction of electroactive counterions, as shown by comparing results for a polymeric strong acid, poly(styre nesulfonic acid), and simple strong acids. The experimental results ag ree reasonably well with Manning's theory, which describes the effect of ionic interactions on the transport of simple ions in the presence of polyelectrolytes. The data agree equally well with a much simpler s emiempirical theory. The experimentally determined limiting value (no supporting electrolyte) of the transport ratio, D/D-0 is 0.53, where D and D-0 are the diffusion coefficients of free hydrogen ion with and without CS. The pK(2) of the carboxyl group of CS is estimated to vary from 3.5 to 5.7 in the range 0.1-0.001 M of ionic strength.