Raman spectroscopy -: A powerful tool for the quantitative determination of the composition of polymorph mixtures:: Application to CaCO3 polymorph mixtures

Raman spectroscopy is an ideal method for identifying polymorphs, because it provides excellent fingerprint spectra specific to each crystal structure. Currently, Raman spectroscopy is successfully used for the quantitative polymorphic analysis of calcium carbonate only in the case of binary mixtures. When a third polymorph is present in the mixture, errors in the quantitative determination increase due to the difficulty in discriminating the different phases in the Raman spectra. In the present work, a new method is developed for mixtures containing more than two polymorphs and tested in the case of vaterite, aragonite, and calcite mixtures of different compositions. It is proved that Raman spectroscopy is a powerful, accurate, and reliable technique for quantitative determination of polymorph mixtures of calcium carbonate. The method can be used for other compounds exhibiting multiple polymorphs.