Effect of Anions on the Solubility of Zwitterionic Amino Acids

The solubilities of glycine, dl-alanine, dl-valine, and dl-serine in aqueous solutions of NaNO3 and of KNO3 are reported at 298.2 K. No pH adjustment or buffer was used in the measurements. The effect of the anion of the electrolyte on the solubility of the amino acid is observed by comparing these results with values reported in the literature for the effect of NaCl and KCl. For each cation, the solubilities of the amino acids are higher with nitrate anion than with chloride anion. With the exception of dl-alanine, the solubility of the amino acid is larger with potassium as the cation than with sodium, at the same concentration of the nitrate salt. This behavior of dl-alanine in nitrate solutions contrasts with literature results using chloride as anion. In the case of chloride as anion, the solubility of the amino acid is always larger in the presence of potassium than in the presence of sodium.