Use of thermo-Raman spectroscopy and chemometric analysis to identify dehydration steps of hydrated inorganic samples - application to copper sulfate pentahydrate

In situ thermo-Raman spectroscopy (TRS) measurements were performed in order to investigate solid-phase transformation of the copper sulfate pentahydrate from room temperature up to 300 degrees C. Band-target entropy minimization (BTEM), a blind-source separation algorithm, was employed in order to identify and reconstruct the pure component spectra of the species involved in the dehydration process. In spite of low signal-to-noise ratio and elevated baseline spectral data, BTEM was successfully utilized to identify and reconstruct four pure component spectra of copper sulfate pentahydrate, trihydrate, monohydrate, and anhydrate, which were formed during this thermally induced process. Subsequent mapping of these four pure component spectral estimates back onto the preprocessed spectra yielded the relative concentrations of each individual species. Finally, the transition temperatures of each dehydration step could be unambiguously deduced from the obtained concentration profile. The current study shows that combined thermo-Raman spectroscopy and chemometric analysis provides an effective tool to determine the dehydration temperatures as well as to identify the structures of each individual species involved in a solid-phase dehydration process. Copyright (C) 2009 John Wiley & Sons, Ltd.