Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Dennis C. Johnson


The development of the technique of pulsed amperometry at a gold electrochemical detector was demonstrated for the detection of sulfur-containing pesticides. The results presented for dimethoate are representative of all compounds studied;Cyclic voltammetry were concluded to be consistent with conclusions that oxidation of sulfur-containing pesticides involves preadsorption of the analyte molecules onto the oxide-free electrode surface during cathodic polarization, followed by the oxide-catalyzed oxidation of the adsorbed molecules at anodic detection potential;Amperometric detection in a flow-injection system was achieved using a two-step pulsed potential technique. The faradaic signal is determined in the two-step waveform at the detection potential for oxidation of the adsorbed analyte simultaneously with formation of the surface oxide. The surface of the gold electrode is cleaned of the gold oxide by stepping to a negative potential at which the reduction of the gold oxide and adsorption of analyte occur. Execution of the waveform in flow-injection detection results in the maintenance of a high and uniform electrode activity for reproducible anodic detection of sulfur-containing pesticides. Detection limits below 100 ppb were determined for most compounds tested;The pulsed technique was applied to the detection of sulfur-containing pesticides separated by reversed phase high performance liquid chromatography (HPLC). The system utilized a C-18 reversed phase column with 50% acetonitrile in acetate buffer at pH 5.0 as the eluent. Detectability was increased significantly using preconcentration from a larger sample onto a C-18 forecolumn.



Digital Repository @ Iowa State University,

Copyright Owner

Aporn Ngoviwatchai



Proquest ID


File Format


File Size

224 pages