Date of Graduation

5-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Degree Level

Graduate

Department

Chemistry & Biochemistry

Advisor

David W. Paul

Committee Member

Bill Durham

Second Committee Member

Ingrid Fritsch

Third Committee Member

Julie A. Stenken

Keywords

Pure sciences, Analytical chemistry, Diffusion, Electrochemical time of flight, Electrochemistry

Abstract

The determination of diffusion coefficients is of fundamental importance to the understanding of electrochemistry and sensors. Developing a method by which diffusion coefficients of Red/ox active analytes can be determined quickly and elegantly, would be a great advancement over presently accepted methods. This dissertation reports the reviving electrochemical time of flight (ETOF), and developing a method that allows for empirical determination of diffusion coefficients from a single measurement. ETOF is a generate and detect experiment where the time an electrochemically generated species takes to transit a known distance is measured and related to the diffusion coefficient of the species. The determined diffusion coefficient of ferricyanide, 7.3(±0.7) x 10-6 cm2/s, was within the 95% confidence interval of the literature value, using the traditional ETOF data treatment. In this dissertation a new treatment of the data, the Moldenhauer treatment, where a diffusional calibration curve is constructed using multiple species of known diffusion coefficient and measuring their transit times at a set distance. The calibration curve constructed in aqueous solutions found the diffusion coefficient of ruthenium(II) hexamine to be within the 95% confidence interval of what has been reported in the literature. The same calibration was also used to determine diffusion coefficients of aqueous probe molecules in a more viscous solution of 20% v/v ethylene glycol and water. Computational modeling was used to further optimize generator pulse widths to allow for a greater linear range of determineable diffusion coefficients. It was shown that an empirically determined aqueous calibration can be used to determine diffusion coefficients in organic solvents. The diffusion coefficient of ferrocene was determined to be 2.4(±0.1) x10-5 cm2/s after modeling directed optimum generator pulse widths. In addition diffusion coefficients were determined for tetrabutylammonium dioxovanadium(V) dipicolinate (3.9(±0.2) x 10─6 cm2/s), and ruthenium (II) bisbipyridine dichloride (9.3(±0.4)x10─6 cm2/s), which do not have published diffusion coefficients presently. Int the future, this same method could be used to determine diffusion coefficients in membranes and complex solvents such as ionic liquids.

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