Automated Ground Water Sampling and Analysis of Trichloroethene Using a 'Universal' Sampling/Analytical System

摘要

Long-term monitoring of sites contaminated with recalcitrant compounds will require the deployment of analytical sensors in an automated system capable of some degree of calibration and quality control. The primary method of providing calibration is to enclose the analytical sensors in a chamber where the environment of the chamber may be controlled. An automated "universal" sampling/calibration/analytical system was developed for mounting analytical sensors in the well or adjacent to the well. The automated universal system allows a sensor to directly analyze the analyte in the water sample or to analyze the analyte in the headspace above the water sample. The ability to analyze the analyte partitioned into the head-space is important for the determination of many volatile species. The analysis of trichloroethene (TCE) is performed by a TCE optrode monitoring the TCE concentrations in the headspace above the water sample. The term optrode refers to a chemically selective fiber-optic sensor. The TCE in the headspace reacts with a colorimetric reagent, producing a colored (red) product. The time history of the development of the colored product is used as the method of determination. The TCE optrode has a limit of detection of 1 part per billion (ppb). There are no interferences from many commonly occurring volatile chlorinated compounds encountered in aquifers such as tetrachloroethene, dichloroethenes, trichloroethane, or dichloro-ethanes. The system was deployed for monitoring TCE concentrations up to 200 ppb at sites in California and Florida.