Date of Award
Doctor of Philosophy
Marc D. Porter
Sensors for the determination of pH have been developed which are based on the immobilization of direct dyes at hydrolyzed cellulosic films. The performance and structural characteristics of the sensors were investigated by a variety of spectroscopic methods, and applications for remote sensing were developed. Films of cellulose acetate were base hydrolyzed in 0.07 M KOH to yield a porous support structure. The structural changes resulting from the hydrolysis on cellulose acetate were probed with infrared internal reflectance spectroscopy. The progress of the hydrolysis reaction was monitored by the changes in vibrational modes of the acetyl group, and other spectral changes indicated changes in film thickness as a result of solvent incorporation. Direct dyes, including Congo Red and C. I. Direct Blue 8, were then immobilized at these porous cellulosic films. The optical response characteristics of the Congo Red pH sensor were characterized, including the UV-visible absorption spectra as a function of pH, the response time as a function of ionic strength and ionic size of electrolyte, the long-term stability of the sensor, the effects of metal-ion interference, and the concentration of Congo Red in the polymer film. The acid dissociation constants of immobilized Congo Red were determined from the pH-dependence of its UV-visible spectra. A calibration method for the sensor was developed which is independent of the concentration of dye in the sensor. The structural characteristics of the sensor were investigated by internal reflectance spectroscopy and resonance-enhanced Raman spectroscopy, and the protonation sites were identified as the two azo groups of Congo Red. Infrared internal reflection spectra of immobilized Congo Red led to the development of a sensor for pH based on infrared spectroscopy. Finally, a two-wavelength fiber-optic photometer, which is based on solid-state sources and detectors, and a fiber-optic probe were developed for pH determinations using Congo Red and C. I. Direct Blue 8 pH sensors. This instrumentation is compact, portable and rugged; it has no moving parts, and it incorporates a reference detector to compensate for intensity fluctuations of the light sources.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Thomas P. Jones
Jones, Thomas P., "Development, characterization, and applications of optical pH sensors supported at cellulosic films " (1990). Retrospective Theses and Dissertations. 9446.