resumo
FT-Raman spectroscopy turns out to be a powerful technique to evaluate the amount of polymorphic and pseudopolymorphic forms in crystalline samples - which is particularly relevant in pharmaceutical sciences. This paper presents a methodology that allows successful quantitative evaluation of the solid-state hydration and dehydration processes, using FT-Raman spectroscopy. All the steps required for a reliable evaluation of the hydration/dehydration process are illustrated for the caffeine system, a particularly challenging system presenting limited spectral differences between the pseudopolymorphs. The hydration process of caffeine was found to occur in a single-step process with a half-life time of ca 13 h, while the dehydration occurs through a two-step mechanism. The critical relative humidity was found to be at ca 81 and 42% for anhydrous and hydrate caffeine forms, respectively. Copyright (C) 2009 John Wiley & Sons, Ltd.
palavras-chave
RAY-POWDER-DIFFRACTION; SOLID-STATE REACTIONS; CRYSTALLINE CAFFEINE HYDRATE; X-RAY; PSEUDOPOLYMORPHIC TRANSITIONS; POLYMORPHIC TRANSFORMATION; PHARMACEUTICAL SOLIDS; QUANTITATIVE-ANALYSIS; MOLECULAR-CRYSTALS; PHYSICAL STABILITY
categoria
Spectroscopy
autores
Nolasco, MM; Amado, AM; Ribeiro-Claro, PJA
nossos autores
Mariela Martins Nolasco
Investigador Auxiliar
Paulo Ribeiro-Claro
Professor Associado com Agregaçãoagradecimentos
The authors acknowledge financial support from the Portuguese Foundation for Science and Technology (FCT) - Unidade de Quimica-Fisica Molecular and Laboratorio Associado CICECO. Mariela M. Nolasco also acknowledges FCT for a research grant - SFRH/BPD/32103/2006.