Date of Award

Fall 1989

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

W Rudolf Seitz

Abstract

The goal of this thesis was to develop and evaluate solvatochromic indicators for fiber optic chemical sensors. Interaction with analyte modifies the polarity of the immobilized indicator environment leading to a shift in their fluorescence spectra. Three systems were studied.

In the first study a cationic fluorescent probe, 5-dimethylaminonaphthalene-1-sulfonamidoethyltrimethylammonium ion (DA$\sp+$), was equilibrated with unmodified- and hydrocarbon bonded-silicas. In solution and unmodified silica, maximum DA$\sp+$ fluorescence shifts to longer wavelengths with increasing percentages of methanol, tetrahydrofuran and acetonitrile in water. On hydrocarbon bonded silicas, however, DA$\sp+$ emission maxima in water occur at shorter wavelengths indicating a very nonpolar environment. This indicates chat the organic fluorophor is excluded from the solvent and experiences primarily a surface environment. Added organic solvent competes with DA+ for the hydrocarbon surface, causing it to interact more strongly with the solvent.

In the second study, 5-Dimethylaminonaphthalene-1-sulfonamidoethyltrimethylammonium ion (AEANS) immobilized on controlled pore glass, cellulose and poly(vinyl alcohol) (PVOH), was shown to respond to cationic surfactants including Dodecyl-, Tetradecyl- and Cetyl-trimethyl ammonium ions. The emission spectrum shifts to shorter wavelengths and increases in intensity with increasing surfactant concentration because surfactant forms an ion pair with AEANS causing its environment to be less polar. Both in solution and immobilized on solid substrates, AEANS responds more sensitively to cationic surfactant with longer hydrocarbon chain lengths. There is no significant response to anionic and nonionic surfactants. AEANS covalently bound to PVOH membranes was coupled to a fiber optic system for reversible in-situ determination of cationic surfactants.

The third system involved a betaine dye, 2,6-diphenyl-4-(3,4,6-triphenyl-N-pyridinio) phenolate (ET30), immobilized in a silicone rubber membrane. At low concentrations immobilized ET(30) fluoresces strongly. Fluorescence intensity decreases and spectra shift to longer wavelengths when the membrane is exposed to increasing percentages of methanol in water. Response is reversible with a response time of several minutes.

All systems studied undergo spectral shifts as a function of analyte concentration. This allows analyte to be related to an intensity ratio measurement at two wavelengths which compensates for changes in variables other than analyte concentration that affect the magnitude of the analytical intensity.

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