ATR FT-IR Imaging Quantitation

As with single-element ATR and transmission mode FT-IR spectroscopy, ATR FT-IR imaging results can be analyzed quantitatively. 

It is important to note that the measurement should operate at least a few degrees above the critical angle to avoid strong dispersion of the refractive index affecting the spectrum. 

Some examples of quantitative analysis of ATR FT-IR imaging include the study of tablet dissolution in water where concentration profiles of hydrox-ypropylmethylcellulose (HPMC) and niacinamide at different stages of the dissolution process were used to understand the drug release mechanism [73]. 

It was demonstrated that concentration profiles of different components can be obtained utilizing the partial least squares method. With concentration profiles readily measurable, it is possible to obtain other quantities such as diffusion type, that is, Fickian versus non-Fickian mechanism of diffusion. The application of in situ ATR FT-IR spectroscopic imaging has been employed to investigate polymer interdiffusion of PVP and polyfethylene glycol) (PEG) under high pressure CO2 [74]. The diffusion mechanism of the system was described based on the spectroscopic imaging data, and it was found that CO2 molecules dissolved in the polymeric system greatly enhanced the interdiffusion process. 

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