In situ measurement of drug transport in porous silica gel

Drug-concentration profiles inside silica alcogels were measured with one-dimensional Raman spectroscopy during wet impregnation. Transparent silica alcogels were impregnated with either paracetamol or ibuprofen by immersing the alcogels in concentrated solutions of paracetamol or ibuprofen dissolved in ethanol as solvent. From the evolution of the drug-concentration profiles (6.4 mm long) (i) the spatial distribution of the drug inside the gel is visualized at any instant of time, (ii) the overall amount of drug accumulated in the gel is quantified, (iii) the binary diffusion coefficient of the drug in ethanol inside the porous gel system is computed and from this (iv) the time required for the impregnation to a certain loading is estimated. We computed the effective binary diffusion coefficient of the drug in the ethanol inside the porous system by fitting Fick's second law to the experimentally measured spatially and temporally resolved concentration data.