Automated Analysis of Trichloroethene and Chloroform

Abstract

Chloroform and trichloroethene (TCE) are two organic contaminants commonly encountered in ground water. TCE, formerly a common cleaning solvent, is usually associated with contaminated aquifers. Chloroform is usually associated with the chlorination of municipal water. The remediation level for TCE in aquifers is typically 5 ppb, therefore, the analytical method employed for monitoring these analytes must be capable of detecting and quantifying the analytes in the low ppb concentration range. The most common analytical methodology for the determination of TCE or chloroform in water is a purge and trap technique for sample introduction into a gas chromatographic system equipped with electroconductivity or mass spectroscopy detector. The instrumentation has a method limit of detection (LOD) of less than 0.5 ppb for TCE and chloroform, however, the expense, size and complexity of the gas chromatographic techniques limit its use outside the laboratory environment. An alternative to the gas chromatographic method for the analysis of select volatile chlorinated compounds in the low concentration range is an analytical instrument based on a halocarbon-specific optrode. The principle of detection is a quantitative, irreversible chemical reaction (modified Fujiwara reaction) that forms visible light-absorbing products. The operational basis of the optrode is the measure of the time history of the development of the colored (red) product formed by the reaction of the target analytes. The optrode has the selectivity and sensitivity for monitoring TCE and chloroform at the low ppb concentration range in the presence of other volatile chlorinated contaminants. The low-power requirements and simplicity of design make it a good choice for remote operations. This paper presents the analytical results (January 2002, to December 2002) of a panel-mounted instrument used to monitor the influent and effluent water of a TCE treatment facility located in Scottsdale, Arizona, and the analytical results of a well-mounted instrument used to monitor ground water (May 2002, to August 2002) at Edwards Air Force Base, California.