FT-Raman and FT-IR spectroscopy and Raman microscopy were employed to identify the structural characteristics of one amorphous and three crystalline phases of nifedipine, a common antihypertension drug of the 1,4-dihydropyridine family. A significant fraction of the nifedipine molecules in the glass are found to be frozen into metastable rotational conformations as a result of melt quenching. Moreover, the effect of relative humidity .RH = 20-80%/ on the onset and rate of crystallization was studied at 40 • C by means of in situ IR and Raman microscopy employing a controlled humidity cell. The nature and the relative abundance of the various crystallization products were analysed on the basis of the corresponding spectra of the neat compounds. Glassy nifedipine is found to crystallize to the thermodynamically stable a-polymorph via a transient metastable b-nifedipine phase. Increasing RH in the range 20-60% is found to favour the surface crystallization of the glass to b-nifedipine. At high RH (80%), b-nifedipine is rapidly converted to a-nifedipine.

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Summary: Poly(ethylene terephthalate) films impregnated with Disperse Red 1 from a supercritical CO2 solution were studied using confocal Raman microscopy. Depth profiles of films dyed for different periods of time were measured using the oil immersion approach and concentration‐depth plots of the relative dye concentration were generated. A one‐dimensional Fickian diffusion model was used to evaluate the diffusion coefficient of the dye from the Raman microscopy data using a non‐linear least squares regression. The calculated diffusion coefficient at 200 bar and 80 °C was 6.75 ± 1.01 × 10−14 m2 · s−1.Typical example of Raman spectra acquired during depth profiling.imageTypical example of Raman spectra acquired during depth profiling.