Effect of anions on the solubility of zwitterionic amino acids

The solubilities of glycine, DL-alanine, DL-valine, and DL-serine in aqueou s solutions of NaNO3 and of KNO3 are reported at 298.2K. No pH adjustment o r buffer was used in the measurements. The effect of the anion of the elect rolyte on the solubility of the amino acid is observed by comparing these r esults with values reported in the literature for the effect of NaCl and KC I. For each cation, the solubilities of the amino acids are higher with nit rate 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 wi th sodium, at the same concentration of the nitrate salt. This behavior of DL-alanine in nitrate solutions contrasts with literature results using chl oride as anion. In the case of chloride as anion, the solubility of the ami no acid is always larger in the presence of potassium than in the presence of sodium.