Densities of glycine and L-serine in aqueous LiNO3, NaNO3 and KNO3 solutions have been measured at 298.15 K with an Anton Paar Model 55 densimeter. Apparent molar volumes, limiting partial molar volumes and transfer volumes have been calculated. Hydration numbers and volumetric interaction coefficients for amino acids were evaluated. The influence of side groups of amino acids and the property of cations on transfer volumes has been discussed in terms of electrostatic interaction and structural interaction. All the transfer volumes of glycine and L-serine are positive and increase with increasing the concentration of salts. The contribution of electrostatic interaction to the transfer volumes is predominant. The reduction in the electrostriction with increasing the concentration of salts was confirmed by the decreased hydration number. Hydrophilic-hydrophilic interaction between the side group of L-serine and ions gives a positive contribution to the transfer volume, which makes the transfer volumes of L-serine larger than that of glycine in the same salt solutions. The transfer volumes of each amino acid in NaNO3 and KNO3 solutions are larger than in LiNO3 solutions. The difference is due to the hard dehyration effect of Li＋. At lower concentrations of the salts the interaction between the amino acids and salts is dominated by 1∶1 form, and at higher concentrations the interaction of 1∶2 form increases.

Key words: glycine, L-serine, nitrate, limiting partial molar volume, partial molar volume of transfer