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Doctor of Philosophy




G. I. Taylor's treatment for the dispersion of mass in a fluid stream is applied to Flow Injection Analysis for the amperometric detection of an injected sample by a tubular electrode. Equations describing the current-time response of the electrode, i(t), the maximum of the current-time curve, i(,p), and the area under the current-time curve, Q(,p), are derived as a function of the volume of the sample, V(,S), the volume of the flow system, V(,R), the flow rate of the fluid stream, v(,f), the coefficient of dispersion, K, and the steady-state current, I(,ss), for the dispersion of a sample in a straight tube under the conditions of laminar flow;The agreement of experimental results with theory is excellent for i(t) and i(,p) at moderately low values of v(,f). A comparison of the experimental current-time curve to theoretical values of i(t) shows that, as predicted by theory, the electrode responds to the concentration of the analyte at the outer boundary of the diffusion layer and not to the mean concentration of the analyte. Experimental values of i(,p) are greater than the theoretical values of i(,p) for higher values of v(,f). This is attributed to the time-dependency of K;The dispersion of a sample in a curved flow system is also described and found to be less than the dispersion of a sample in a straight flow system for the same values of V(,S), V(,R), and v(,f). The value of K for a curved flow system could not be determined theoretically; however, equations for i(,p) for a straight flow system can be used to calculate i(,p) for a curved flow system if an experimentally determined value of K is used;Experimental and theoretical values of Q(,p) are in excellent agreement. The value of Q(,p) is independent of the degree of dispersion and dependent only on V(,S), v(,f), and I(,ss). Both i(,p) and Q(,p) are linear functions of the concentration of the analyte. The measurement of Q(,p) is, however, more advantageous than the measurement of i(,p) in that Q(,p) is independent of dispersion.(,);The steady-state behavior of the tubular electrode is also described and the validity of the concept of a flow-rate independent component of the steady-state current is brought into serious question. The concept was originally proposed to explain the nonzero intercepts obtained for linear extrapolations of plots of I(,ss) versus V(,f)('1/3). The nonzero intercepts are concluded to be mathematical artifacts of inaccurate data analysis rather than the results of an electrochemical phenomenon.



Digital Repository @ Iowa State University,

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Peter Lawrence Meschi



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210 pages