Interaction of DL-threonine with NaCl and NaNO3 in aqueous solutions: emf measurements with ion-selective electrodes

The interactions between DL-threonine and NaCl or NaNO3, at T=(298.15 +/- 0.02) K, have been investigated by measuring e.m.f. values, with ion-selective electrodes (ISE), in electrochemical cells. The electrochemical cell employed consisted of two ion-selective electrodes, a cation and an anion ion-selective electrode, against a double junction reference electrode. The e.m.f. values thus obtained were used to calculate the activity coefficients of DL-threonine in aqueous electrolyte solutions. Measurements were performed up to molalities m of 1.4 mol.kg(-1) for DL-threonine and 1.0 mol.kg(-1) for the electrolyte. Experimental data for the activity coefficients of DL-threonine in {NaCl(m(S)) + DL-threonine(m(A))}(aq) and {NaNO3(m(S)) + DL-threonine(m(A))}(aq) measured at T=(298.15 +/- 0.02) K are reported. The results of the activity coefficients of DL-threonine in the presence of two different electrolytes with a common cation are compared and discussed. The results of the activity coefficients of DL-threonine in {NaCl(m(S))+ DL-threonine(m(A))}(aq) are also compared with those of the DL-valine in {NaCl(m(S)) + DL-valine(m(A))}(aq) reported previously.((1)) The results show that the presence of an electrolyte and the nature of its anion have a significant effect on the activity coefficient of DL-threonine in aqueous electrolyte solutions. The results also show that the chemical structure of an amino acid has a significant effect on its interactions with an electrolyte. (C) 1997 Academic Press Limited.