Control of molecular weight selectivity in electrode modifications based on phase-inversion cellulose acetate...

Modified electrodes with size selectivity are required for electrochemical blosensors and for analysis of biological samples. The phase-inversion process for making reverse osmosis membranes is used to make modified electrodes with the goals of decreasing thickness, improving response time, and understanding the influence of both casting solution composition and casting conditions on the resultant membrane's porosity. Poly(ethylene glycol) esters of ferrocene-carboxylic acid are used for the determination of the membrane's response time, selectivity, and structure. It is shown that there is an optimum composition range of greater than 95% acetone, less than 2% cellulose acetate, and less than 5% aqueous Mg(CIO4)2. This composition range gives the minimum response time (greater than 90% of maximum signal is obtained in less than 7 min), maximum reproducibility (less than 20% relative error), and best size selectivity in the few thousand daltons range.