Simple Voltammetric Method for the Determination of the Partition and Diffusion Coefficients in Solvent Polymeric Membranes

For feedback controlled monitoring of the popular anesthetic drug propofol we used an organic membrane-coated voltammetric sensor.¹ The membrane coating prevents electrode fouling, and provides outstanding detection limit and selectivity for the voltametric working electrode that is adequate for continuous monitoring of propofol in whole blood in the presence of physiologically relevant interferences.

The detection limit of the voltametric sensor is controlled by diffusion coefficient (D) and the concentration of the analyte in the membrane (c_M), where c_M is a function of membrane/solution partition coefficient (P). The selectivity of the membrane-coated sensor, on the other hand, depends on the partition coefficients of the analyte and interfering compounds.

To assess the attainable detection limit and selectivity of the membrane coated sensor the diffusion and the partition coefficients have to be known. For the determination of the diffusion coefficients in the membrane it has been loaded with the analyte and the steady state current of a membrane coated planar electrochemical cell with a carbon fiber ultra microelectrode has been recorded in air (D=i⁄(4nFc_Mr)). By placing the membrane-coated planar electrochemical cell into a solution the concentration of the analyte in the membrane will be determined by its partition coefficients. From cyclic voltammetric experiments with the membrane-coated sensor in an analyte solutions one can calculate the partition coefficient of the analyte.

In our contribution we discuss the unique advantages of the voltammetric method and report the partition coefficients of a variety of compounds (e.g., propofol, ascorbic acid, p-acetamido phenol) between plasticized PVC membranes and aqueous electrolytes as well as the diffusion coefficients of these compounds in the membranes.

1. Kivlehan, F.; Garay, F.; Guo, J. D.; Chaum, E.; Lindner, E., Anal. Chem. 2012, 84 (18), 7670-7676.