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Polymorphism of L-glutamic Acid: Influence of the Additive Ammonium Sulphate upon the Phase Change between α- and β-polymorphs
T. K. P. Nguyen, C. Q. Khuu, Đ. T. Nguyen, T. D. T. Tran, T. T. H. Trinh, T. T. H. Le, V. D. Trinh, T. H. N. Le, T. K. D. Hoang, T. T. Phan and A. T. Nguyen

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ABSTRACT

The effect of salt additive (NH4)2SO4 on the phase transformation of L-glutamic acid was investigated in cooling crystallization. L-glutamic acid has two kinds of polymorph including α-form and β-form that are known as the metastable and stable form, respectively. In cooling crystallization, the α-form was initially generated, after that it slowly transformed into the β-form in the solution, where the phase transformation required at least 25 h for completion. However, the present study indicated that the phase transformation of L-glutamic acid was significantly promoted as using the salt additive (NH4)2SO4, where it completely transformed within 12 h as using salt additive of 4 g/l. That means the phase transformation was markedly accelerated more than 2.0 times as using the salt additive. Here, the solute concentration during the phase transformation was monitored by the UV/Vis spectroscopy, while the shape and crystal fraction of α- and β-form were confirmed by the optical microscope and FT-IR spectroscopy, respectively.

Key words: Crystallization, polymorphism, phase transformation, additive effect

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