Polymer Membrane Based Optical and Electrochemical Anion/Polyanion Sensors.

Abstract

Polymer membrane based optical and electrochemical anion sensors employing metalloporphyrins as ionophores are attractive tools for the detection of specific anions in environmental and biological samples. In this dissertation, sensors with selectivity toward fluoride and nitrite have been developed and evaluated. In addition, a new application of previously reported polyanion sensors has been demonstrated, specifically to detect the presence of a high charge density contaminant, oversulfated chondroitin sulfate (OSCS), in biomedical heparin preparations. Finally, the working mechanism of a polymer membrane based gas sensor toward nitric oxide (NO) has been examined. Dimer formation of Al(III) porphyrins when in contact with fluoride has been verified by mass spectrometry and UV/visible spectroscopy. A new polymethacrylate copolymer with covalently attached Al(III) porphyrins has been synthesized and characterized to eliminate dimer formation when using Al(III) porphyrins as fluoride ionophores in electrochemical and optical sensors. Prolonged lifetime (14 days) of sensors has been achieved when employing this new polymer as a membrane ingredient. However, spectroscopic evidence suggests that dimer formation of the Al(III) porphyrins linked to the copolymer can still occur. Co(III) porphyrins are known as nitrite selective ionophores when used in a conventional membrane electrode configuration. In this work, a coated wire electrode system employing a Co(III) porphyrin has been developed and optimized. The sensor exhibits lower detection limit (2.3 x 10-6 M) but shorter lifetime compared to conventional electrodes. An optical nitrite sensing system based on anion/proton co-extraction chemistry has also been developed using Co(III)porphyrin ionophore. Potentiometric polymer membrane based polyanion sensors have been applied as a screening tool for the detection of OSCS in commercial heparin preparations based on the difference charge density of the polyanion species, with a detection limit of 0.2 wt%. Quantification of this contaminant has also been achieved by the new potentiometric method. An unusually low detection limit toward NO gas has been observed when employing Co(III) porphyrin as a receptor in the polymer membrane based electrodes. The working mechanism of this potentiometric NO response has been elucidated to involve a redox reaction of NO with the Co(III) porphyrin in the organic membrane of the sensor.