A New Crystalline form of Monosodium l-Glutamate

A new crystalline form of monosodium l-glutamate, which is different from the known monosodium l-glutamate monohydrate crystal in external appearance, density, X-ray diffraction pattern, solubility, and water of crystallization, has been crystallized from ca. 73 weight per cent aqueous methanol solution at ca. 18°C. It was identified as the dihydrate from the determination of water of crystallization based on Karl Fischer′s method. The newly found crystals are extremely unstable in air, aqueous solution, and the mother liquor, because of rapid transformation into the stable monohydrate, whereas they can be kept in a considerably stable condition in absolute ethanol and acetone.