Chemical Image Fusion. The Synergy of FT-NIR and Raman Mapping Microscopy To Enable a More Complete Visualization of Pharmaceutical Formulations

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Abstract
The pharmaceutical industry uses successfully both FT-NIR and Raman microscopy to produce chemical images of solid dosage forms, typically in troubleshooting roles. However, due to the chemical composition of the formulations,it is not always possible to describe the entire chemical formulation by using a single spectroscopic method. As Raman and NIR spectroscopies are complementary in nature, their combined usage offers the opportunity to describe heterogeneous mixtures in more detail. A novel sample referencing approach has been developed that allows data to be acquired from exactly the same area of the sample using both Raman and FT-NIR microscopies. The optimum images for the components are then overlaid, which gives rise to a combined chemical image that visually describes the entire formulation. We have named this approach chemical image fusion (CIF). CIF has been applied to two examples. The first shows how a simple formulation was used to validate the CIF approach. In the second, CIF allowed an entire formulation to be visualized and the cause of tabletting problems determined. CIF provides increased confidence in the results generated by each individual technique and offers a more powerful method for the evaluation of pharmaceutical formulations.