Ternary phase diagram and the formation mechanism of two distinct solid solutions of amino acid systems: l-Valine/l-norvaline and l-valine/l-alanine

•The ternary phase diagrams of l-Val/l-Nva/water and l-Val/l-Ala/water at 293.15 K were determined.•Complete solid solution and partial solid solution were formed.•Molecular investigation of the complete solid solution was developed.•Fractional crystallization were verified as an effective purification method for solid solution system.