An electrochemical method for measurement of mass transport in polymer membranes using acetaminophen as a model system

An electrochemical approach has been used to model and measure acetaminophen transport through a microporous polycarbonate membrane. The dynamic response of a membrane covered planar electrode system was investigated to derive a simplified middle point formula, the time at which amperometric current reaches half steady state value, that provided reliable solute diffusion coefficients. Experimental values may be noise-contaminated; when this noise is significant, the diffusion coefficient by this method needs to be refined. Here a direct simulation method with a bipartite mathematical expression for current transient was used, which fitted calculated current transients to experimental data. A best fit was reached by minimising the standard deviation between the simulated and experimental current profiles. Mathematically, the simulated curve was linear operated, i.e. shifted and stretched vertically, as well as shifted and stretched horizontally to coincide with the experimental curve. The single point formula, bipartite expression and simulation approach allowed extraction of accurate diffusion values from a previously reported approximated method. The computation approach is not only valid for membrane covered electrodes, but is suitable for other experimental set ups where a one-dimensional Fickian diffusion model is valid, for example, for axial diffusion through cylindrical geometries.