Journal
JOURNAL OF PHARMACEUTICAL SCIENCES
Volume 95, Issue 11, Pages 2486-2498Publisher
WILEY-BLACKWELL
DOI: 10.1002/jps.20719
Keywords
terahertz pulsed spectroscopy (TPS); low-frequency Raman spectroscopy; far-infrared; sulfathiazole; polymorphism; phase transitions; differential scanning; calorimetry (DSC); high-speed DSC; physical characterization; lattice vibrations
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The far-infrared properties of all five known polymorphic forms of the drug sulfathiazole have been studied by terahertz pulsed spectroscopy and low-frequency Raman spectroscopy. The observed spectra of the different polymorphs are distinctly different. Terahertz pulsed spectroscopy proves to be a rapid and complementary alternative to other physical characterization techniques reported in the literature for distinguishing between the five forms. Variable-temperature measurements (293-473 K) of all polymorphic forms have been performed. The phase transitions observed have been related to thermal analysis data. Form I is the form stable at high temperature of sulfathiazole with a melting point of about 475 K. Form II melts at around 470 K and recrystallizes at higher temperatures to form I. Forms III, IV, and V all convert to form I via a solid-solid phase transition at temperatures below 450 K. The phase transitions can be monitored by terahertz pulsed spectroscopy. Polymorphic impurities of the samples can be detected in the room temperature spectra and their effect on the phase transition behavior can be studied. (c) 2006 Wiley-Liss, Inc. and the American Pharmacists Association.
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