The use of in situ tools to monitor the transformation of a polymorphic material has the potential to provide unique information about the mechanism and rate of transformation of the polymorphs. In this paper, the solution mediated transformation between α and β form p-aminobenzoic acid (PABA) was investigated in detail. Solubility of α and β form PABA in pure ethanol was also reported for the first time, allowing the accurate determination of the transition temperature of 13.8 °C. For the transformation experiments, Raman spectroscopy and Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy were used to in situ monitor the solid phase concentration and liquid concentration, respectively; Focused Beam Reflectance Measurement (FBRM) was used to in situ track the changes in the size and morphology of the particles. The observed changes were confirmed using PVM in-process imaging. It was proved by solubility data and transformation experiments that the relationship between α and β form is enantiotropic.
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Hao et al. (2011) studied this question.
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