Solubilities of amino acids in water at various pH values under 298.15 K

摘要

The objective of this study is to investigate the solubility behavior of amino acid in water for various pH values at 298.15 K. In the experimental part, a spectrophotometer was employed to analyze the solubility data for four amino acids of DL-alanine, L-leucine, L-isoleucine and L-serine in water. It was observed that the pH effect, changing from 2 to 10 adjusted by HCl or NaOH, is significant to the solubility data. This is due to the fact that amino acids appear in several forms, which are neutral zwritterions, amino acid cationic and anionic species, during the dissolution process. These are not only equilibrated with each other but also with hydrogen ions. In the theoretical part, physical and chemical equilibria were considered simultaneously to model the solubility of amino acids in water. A calculation method combined of chemical model, activity coefficient model and equilibrium criterion was used. In this study, NRTL model was used to describe the non-idealities in the solution. The calculated results agree well with the experimental data.