Date of Award

6-1997

Document Type

Union College Only

Degree Name

Bachelor of Science

Department

Chemistry

Language

English

Abstract

The goal of this thesis project was to create a Methylene Blue (MB) doped sol-gel fiber-optic fluorescence sensor. Ideally this sensor would be capable of detecting changes in sulfite concentration in solution continuously and reversibly. In aqueous solution, MB, a redox indicator, is converted from a bright blue color to the colorless leuco-MB species upon exposure to sulfite or other reducing agents. This reaction is reversible in the presence of an oxidizing agent Therefore, if MB can be immobilized properly, it would make a suitable reversible indicator for the sulfite anion in solution. The method of MB immobilization employed in this project was the sol-gel method. Organic solutes can be physically entrapped in sol-gels without being altered chemically. In this project, sol-gels were prepared by the hydrolysis and condensation of either tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS). MB doped sol-gels were prepared using both TMOS and TEOS as precursors. Leaching of MB from these sol-gels does not appear to occur in neutral aqueous solution. The MB doped sol-gels prepared are responsive to the sulfite ion in solution; however, they are significantly less responsive to oxidizing agents. Blue MB is not readily regenerated from leuco-MB within the sol-gels. Moreover, the MB converts to the colorless leuco-MB form within the sol-gels over time even in the presence of oxidizing agents. Hence, this system requires further fundamental study before it can be used in the preparation of a reusable sol-gel fiber-optic fluorescence sulfite sensor. This system, however, is currently suitable for use as a disposable sulfite sensor.

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