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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