Effect of the anion and the cation of an electrolyte on the activity coefficient of dl-alanine in aqueous solutions

The effects of the nature of the cation and the anion of three electrolytes on the activity coefficient of dl-alanine in aqueous solutions at 25°C, are investigated. The electrolytes studied are NaCl, KCl and NaNO3. The study covers up to 1.6 molality dl-alanine and up to 1.0 molality electrolyte. An electrochemical cell with two ion selective electrodes, a cation and an anion ion selective electrode, versus a double junction reference electrode, was used to measure the activity coefficients of dl-alanine in aqueous electrolyte solutions. Experimental data for the activity coefficients of dl-alanine in water+KCl+dl-alanine and water–NaNO3+dl-alanine systems measured at 25°C are reported. Experimental data for the activity coefficients of dl-alanine in water+NaCl+dl-alanine system were obtained from a previous study. Measurement of activity coefficients of amino acids in aqueous electrolyte solutions: experimental data for the systems H2O+NaCl+glycine and H2O+NaCl+dl-alanine at 25°C. Ind. Eng. Chem. Res. 35, pp. 2735–2742.]. The results of the activity coefficients of dl-alanine in the presence of different 1:1 electrolytes are compared and discussed. The results show that the nature of both the cation and the anion of an electrolyte have significant effects on the activity coefficients of dl-alanine in aqueous electrolyte solutions.