FTIR imaging for the characterization of controlled-release drug delivery applications

The diffusion of nicotine in ethanol/water mixtures into an ethylene-vinyl acetate (EVA) copolymer membrane was studied by FTIR imaging. The spatial and temporal distribution of each component in the EVA membrane was demonstrated in the FTIR images. The concentration profiles extracted from these images showed that segregation occurs during diffusion. Nicotine diffuses into EVA ahead of the solvent for 0-60 wt% ethanol/water mixtures, but the segregation behavior changes as the ethanol in the solvent increases to 80 wt%; for the 80 wt% ethanol solvent, D(2)O leads the diffusion front, and for the 100% ethanol solvent, ethanol diffuses into EVA first. The initial swelling rates were calculated from the concentration profiles, and an exponential trend with increasing ethanol in the solvent was observed. The concentration profiles were also used to calculate average diffusion coefficients for the overall solutions and specifically for nicotine. The relative intensities of the aromatic ring stretching bands of nicotine in solution indicate that the solvation properties in pure ethanol and water are not equivalent; a pseudo-conjugation scheme between water and nicotine was proposed to account for this difference. Examination of the intensity of the carbonyl band of the EVA film revealed an interaction with the solvents by hydrogen bonding.