Diffusion of transdermally delivered nitroglycerin through skin mimetics using photoacoustic and attenuated total reflectance spectrometry

Infra-red (IR) photoacoustic spectroscopy (PAS) and attenuated total reflectance spectroscopy (ATR) were used to determine the diffusion coefficient of transdermally delivered nitroglycerin (NG) within a polyethylene glycol (PEG) saturated microfibre filter. The build-up of the drug within the probed layer was measured by monitoring the change in IR bands as a function of time. The absorbance was assumed to be directly proportional to the drug concentration. The diffusion coefficient of the nitroglycerin within the filter was calculated by fitting the theoretical diffusion model to the experimental diffusion profile. The diffusion coefficient of nitroglycerin within the filter was calculated to be (3.83(plus-minus)0.40)×10^-7 cm^2 s^-1 and (4.31(plus-minus)0.60)×10^-7 cm^2 s^-1 using PAS and ATR, respectively. The close agreement of the two values indicates the reliability of the techniques and diffusion models.