Date of Award
Doctor of Philosophy
Dennis C. Johnson
Several aspects of the application of pulsed amperometric detection (PAD) to carbohydrate analysis are addressed. The mechanism of glucose oxidation at a gold electrode was determined by cyclic voltammetry at a rotating disc electrode in the first study. Glucose oxidation was concluded to be catalyzed by a hydrous gold oxide which was formed on the surface of the electrode in alkaline solution at potential values between -0.4 and 0.6 V versus the normal hydrogen electrode. The mechanism of glucose oxidation changed from a mass transport limited reaction with n = ca. 8 equiv mol[superscript]-1 to an electron transfer limited reaction with n = ca. 2 equiv mol[superscript]-1 as a consequence of increased glucose concentration. The change in the mechanism was concluded to result from increased competition between glucose molecules for adsorption at the catalytic sites on the gold electrode as the concentration of glucose was increased;The second study demonstrated a method for determining glucose by PAD in low capacity buffers having neutral and acidic pH values. A transient condition of alkalinity was generated within the diffusion layer of gold electrodes by stripping of surface oxide and reduction of dissolved oxygen prior to the application of the detection potential for glucose in the PAD waveform. The transient alkaline state effected the formation of the hydrous gold oxide which was necessary for the anodic detection of glucose. The method was applied to the direct determination of glucose in a continuous glucoamylase assay in the presence of the active enzyme and the starch substrate at pH 4.8. This method for glucoamylase activity was accurate, more precise, and much faster than the traditional ferricyanide assay;The final two studies demonstrated methods for determining starch by flow injection and maltooligosaccharides by chromatographic analysis with single glucose calibration curves by placing an immobilized glucoamylase reactor in series with the PAD detector cell. Starch and maltooligosaccharides were nearly quantitatively (96%) converted to glucose prior to being detected by PAD. The sensitivity of PAD for soluble starch increased 26-fold by first passing the starch through the glucoamylase reactor. The methods were used to determine total carbohydrate in beer samples and maltooligosaccharides found in corn syrup.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Larry Arnold Larew
Larew, Larry Arnold, "Quantitation of maltooligosaccharides and determination of glucoamylase activity using pulsed amperometric detection for glucose " (1988). Retrospective Theses and Dissertations. 8864.