Date of Award
Doctor of Philosophy
Chemical and biological sensors are often constructed as multilayer systems in which a base electrode is separated from sample by one or more polymer membranes. Well-known examples include blood glucose sensors and immunosensors, which are used to diagnose and monitor medical conditions for millions of patients each year. More recently, a plasticized PVC membrane-coated voltammetric sensor for the anesthetic propofol (chemical name: 2,6-diisopropyl phenol, abbreviation: DIPP) has been developed. The response of this sensor is strongly influenced by the diffusion coefficient of DIPP (Dm) in the PVC membrane and the partition coefficient of DIPP (Pma) between the membrane and aqueous solution. Sensor selectivity is controlled by the ratio of the Pma of DIPP vs the Pma of potential interferents (e.g. acetaminophen (APAP)).Planar electrochemical cells (PEC) with carbon fiber working electrodes were used to voltammetrically measure Dm in plasticized PVC membranes and plasticizer solutions. To determine Pma values for a variety of analytes, the concentrations of these analytes were measured with the PECs before and after the membranes were equilibrated with aqueous solutions. The Dm and Pma values of ferrocene carboxylic acid (FcCOOH), DIPP and APAP were measured. PVC membranes and plasticizer solutions were made with either 2-nitrophenyl octyl ether (oNPOE), bis(2-ethylhexyl) sebacate (DOS), or 1-octanol (octanol). Membranes were cast with 1/2, 1/4, or 1/8 PVC/plasticizer ratios. Dm increased with decreasing plasticizer viscosity and with decreasing PVC/plasticizer ratio, in agreement with the Stokes-Einstein model. However, the Dm of APAP in plasticizer solutions were only about half their theoretically estimated value, while the Dm of DIPP in plasticizer solutions were almost twice their theoretically estimated value. Pma values strongly depended on the lipophilicity of the analyte and the plasticizer. Pma of DIPP (very lipophilic) increased with plasticizer lipophilicity, while the Pma of APAP (less lipophilic) decreased with plasticizer lipophilicity.The voltammetric methods for measuring Dm and Pma are a useful complement to conventional methods where those are complex or unfeasible. The methods support the characterization and optimization of membrane-coated sensors and provides a simple possibility for the quantification of diffusion and partition coefficients in other applications of soft polymer membranes.
dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.
Sheppard, James Bereman, "Voltammetric Determination of Diffusion and Partition Coefficients in Plasticized Polymer Membranes" (2016). Electronic Theses and Dissertations. 1494.