Activity coefficients in (electrolyte + amino acid)(aq) The dependence of the ion-zwitterion interactions on the ionic strength and on the molality of the amino acid analysed in terms of Pitzer's equations

Activity coefficients of electrolyte and amino acid in the systems (water + potassium chloride +dl -valine) at T=298.15 K and (water + sodium chloride +l -valine) at T= 308.15 K

“…Most measurements of the activity coefficients of amino acids in aqueous electrolyte solutions have been made by the isopiestic (3)(4)(5) and the electrochemical methods. (6)(7)(8)(9) The only direct experimental method for determining the activity coefficient of a solute in an electrolyte solution is by means of electromotive force measurements. Electrochemical cells with ion-selective electrodes are important tools that are used to measure the activity coefficients of the electrolytes.…”

A steady-state shifting technique for the potentiometric method: Application to supersaturated solutions

“…Experimental data of II ± / I ± from the present study for the system (glycine + NaCl + H 2 O) in the under-saturated region with respect to glycine were compared with previously published data (Khoshkbarchi and Vera, 1996b;Phang and Steel, 1974;Rodriguez-Raposo et al, 1994;Scherier and Robison, 1971). Table 3 shows the % mean deviation between our data and those from each source.…”

“…The activity coefficient of glycine is related to the mean ionic activity coefficient of NaCl through the cross-differential relation (Khoshkbarchi and Vera, 1996b): -Raposo et al (1994) 0.01-2.5 0.1-2.0 27 0.26 Potentiometric Phang and Steel (1974) 0.01-1.0 0.5-2.0 12 0.26 Potentiometric Scherier and Robison (1971) 0.1-2.5 0.1-3.3 111 0.51 Isopiestic …”

Activity coefficients of glycine in aqueous electrolyte solutions: experimental data for (H2O+ KCl + glycine) atT= 298.15 K and (H2O + NaCl + glycine) atT= 308.15 K

“…Apart from some inaccurate methods, such as the freezing temperature method, (4) two major techniques, which have been commonly used, are the isopiestic method (5)(6)(7) and the electrochemical method. (8)(9)(10) Electrochemical cells are an essential tool for experimental studies of solutions containing electrolytes and have been widely used for the measurement of their thermodynamic properties. (11,12) In contrast to the isopiestic method, electrochemical methods deal directly with the thermodynamic properties of the electrolyte.…”

“…Most of the studies, which have reported the measurement of the activity coefficients of amino acids in aqueous electrolyte solutions using ion-selective electrodes, have used a cation ion-selective electrode only, against a reference electrode. (9,10,13) In these studies, the difference between the potentials of the ion-selective electrode and the reference electrode was calibrated with the mean ionic activity coefficient of the electrolyte in an aqueous electrolyte solution without the amino acid. Since in this method of measurement the effect of counter-ion of the electrolyte is neglected, it may lead to erroneous results.…”