This work is supported by project Project PEst-C/EQB/
LA0020/2013, financed by FEDER through COMPETE -
Programa Operacional Factores de Competitividade and by
FCT - Fundação para a Ciência e a Tecnologia.
Using a water activity instrument meter, water activity in aqueous solutions of DL-alanine, glycine, or L-serine,
with potassium chloride, molality ranging from 0.0 to 3.0, has been measured at 298.15 K. The reliability
of the method was checked comparing the experimental data with literature values. The method proved to
be accurate, and the water activities measured for water + amino acid systems are reproducible when
compared to the data reported using the isopiestic method. Additionally, a simple theoretical approach applied
to those binary systems enabled the calculation of unsymmetric molal amino acid activity coefficients in
high agreement with the values found using the isopiestic measurements. Finally, the usefulness of the
ternary data to extend the capabilities of thermodynamic models to higher salt and amino acid concentrations
was briefly discussed.
Water activity in aqueous solutions of DL-alanine, glycine, or L-serine, with ammonium sulfate, molality ranging from 0.5 to 5.0, have been measured at 298.2 K. The new experimental data was correlated using three different theoretical schemes such as Zdanovskii-Stokes-Robinson, its extension, or the Clegg-Seinfeld-Brimblecombe approach, with global average absolute deviations in the calculation of the osmotic coefficient of 3.46 %, 0.93 % and 1.95 %, respectively. The extended Zdanovskii-Stokes-Robinson method also enabled the prediction of unsymmetric molal activity coefficients of the electrolyte, in fair agreement with the experimental values found from literature measured by an electrochemical method. It is evidenced the usefulness of the experimental ternary data measured to extend the capabilities of thermodynamic models to higher salt and amino acid concentrations.
