Rener Wang

Date of Graduation

1998

Document Type

Thesis

Abstract

A Universal Amperometric Membrane-Covered Gas-Sensing Electrode System has been designed which can be used with a wide variety of electrochemical sensors. The system is composed of two parts: an electrode detection unit consists of an Intel 8051 microprocessor as the control unit which receives operational commands through the serial port of a personal computer. The assembly language has been written and is embedded in a 32K EPROM and the data collected are temporarily stored in a 32K RAM. A potentiostat with an auto-adjustable 100 nA to 100 {dollar}\\mu{dollar}A range is used to polarize the electrode. A 12 bit D/A convertor with 1 mV resolution can accurately control the potential between {dollar}-{dollar}2 V and +2 V, and a high resolution 12 bit A/D convertor is used to digitize the electrode signal. The system has been programmed for seven electrochemical techniques which can be applied to any amperometric sensor. The collected binary code is transferred to the PC via an RS-232 serial port. Software programmed with C language is operated on a Windows 95 platform and has a GUI front-end to allow the operator to select one of the seven methods as well as modify the appropriate parameters to conduct the experiment. The selected parameters are transferred to the electrode detection unit to automatically control the measurement. The collected data are shown graphically and numerically on the screen and can be saved, retrieved or printed. This Universal Sensor System has been used to measure low levels of oxygen, ozone and chlorine dioxide in water. Double potential step chronocoulometry has been used to eliminate the stirring effect commonly encountered with steady state amperometric membrane electrodes. Calibration curves are linear and detection limits of 30 {dollar}\\mu{dollar}g/L and 50 {dollar}\\mu{dollar}g/L were achieved for chlorine dioxide and ozone, respectively.

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