Journal
INTERNATIONAL JOURNAL OF PHARMACEUTICS
Volume 221, Issue 1-2, Pages 123-141Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S0378-5173(01)00677-9
Keywords
all-trans retinoic acid; tretinoin; solid-state characterisation; phase transition
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Thermoanalytical (differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (TG/FTIR)) and spectroscopic (X-ray diffraction (XRD), ultraviolet-visible (UV-Vis), mass spectrometry (MS) and Fourier transform infrared diffuse reflectance (DRIFT) measurements have been used to characterise solid-state retinoic acid (RA) from a chemico-physical point of view. Between 130 and 160 degreesC, a phase transition takes place that does not correspond to the transition between the known monoclinic and triclinic phases (DSC and XRD evidence). By annealing in air tin the 130-160 degreesC temperature range and for different times), an exothermic oxidative degradation occurs that, depending on the thermal treatment, competes with the mentioned phase transition (TGA evidence). Spectroscopic techniques (UV-Vis, MS and DRIFT) allow one to conclude that the new solid phase is still constituted by retinoic acid with a different orientation of the side chain. Finally, RA does not undergo stable melting: the fragmentation patterns, both in air and in nitrogen, have been examined by TG/FTIR. (C) 2001 Elsevier Science B.V. All rights reserved.
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