Regions of interest in FTIR imaging applications: Diffusion of nicotine into ethylene-co-vinyl acetate films

Effective image analysis of dynamic processes, such as diffusion and dissolution, requires precise reporting of component locations in space and time. An improved method for analyzing FTIR images is described which employs hypothesis testing in the spatial and temporal domains. Changes in the observed absorbance (over space and time) are revealed by comparison to a reference statistic, which can be tailored by choosing the size of a region of interest. This improved analysis method was used to compare the rates of diffusion of nicotine into poly(ethylene-co-vinyl acetate) film from aqueous solutions containing anionic and nonionic surfactants. Compared to a solution without surfactant, sodium dodecyl sulfate inhibited the uptake of nicotine from aqueous solution whereas Tween 40 enhanced the uptake. The nicotine diffusion rate also showed a dependence on the length of the hydrophobic segment of nonionic surfactants. These results demonstrate the roles of solubilization, wetting, and viscosity on diffusion-controlled drug release.