Instrumentation for the Detection of Halocarbons in Groundwater. Final Report, January 1, 1989 to December 31, 1989.

摘要

An instrumentation strategy has been identified for eventually achieving the reliable and quantitative detection of trace halocarbons in groundwater samples. The instrumentation approach relies upon the initial photoelectrochemical (PEC) degradation of the halocarbon to be detected, immediately followed by its potentiometric electrochemical detection as chloride species. Initial PEC degradation of trace halocarbons was achieved using illuminated n-TiO2 (anatase). Two illumination sources (365 and 254nm) were simultaneously used to promote electron excitation from the anatase valence to conduction band to obtain comparative halocarbon degradation rates. PEC degradation rates for the halocarbons trichloroethylene (TCE) and vinyl chloride (VC) were found to progressively decrease with time. The observation suggested that the initial halocarbon concentration, prior to the inception of PEC degradation, might be determined from the measured degradation rate after a defined photolysis time. The expectation was confirmed by comparing halocarbon degradation rates for simulated contaminated groundwater containing known amounts of halocarbons. As might be expected, PEC degradation rates for halocarbons occurred more rapidly at shorter wavelengths. Such differences in photodegradation rates suggested a means of differentiating between these two halocarbons.