INTERACTION OF SODIUM POTASSIUM IONS WITH KAPPA- AND LAMBDA-CARRAGEENAN IN AQUEOUS SOLUTIONS WITH AND WITHOUT ADDED SALT

The interactions of small ions with the sodium and potassium salts of k- and ʎ-carrageenan were studied by measuring the counterion and coion activity coefficients in aqueous solutions of the polyelectrolytes with and without an added simple electrolyte. In solutions without added salt, the counterion activity coefficients for the X forms were relatively constant with varying concentration, while for the k forms they increased with dilution. The values for the sodium carrageenans were smaller than for the corresponding potassium salts, and were smaller for the X form than for the k form when the counterions were the same. These results indicated a greater amount of counterion binding for the ʎ-carrageenans, and that more sodium than potassium was bound. For solutions containing an added simple electrolyte, counterion activity coefficients were again lower for the X-carrageenans. Counterion activity coefficients decreased with increasing polyelectrolyte concentration at constant simple salt concentration and decreased with decreasing salt concentration at constant polymer concentration. The additivity rule was best obeyed when the ratio of simple salt to polyelectrolyte concentration was high or low and the greatest deviation was evidenced when the salt and polyelectrolyte concentrations were approximately equal. Coion activity coefficients were slightly lower than those for the pure simple salt solutions and followed the same general trends as the counterion activity coefficients. © 1969, American Chemical Society. All rights reserved.