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A Total Organic Carbon (TOC) Analyzer has been developed for a Life Sciences Risk Mitigation Flight Experiment to be conducted on Spacehab and the Russian space station, Mir. Initial launch is scheduled for December 1996 (flight STS-81). The analyzer will be tested on the Orbiter in the Spacehab module, including when the Orbiter is docked at the Mir space station. The analyzer is scheduled to be launched again in May 1997 (STS-84) when it will be transferred to Mir. During both flights the analyzer will measure the quality of recycled and ground-supplied potable water on the space station. Samples will be archived for later return to the ground, where they will be analyzed for comparison to in-flight results. Water test samples of known composition, brought up with the analyzer, also will be used to test its performance in microgravity. Ground-based analyses of duplicates of those test samples will be conducted concurrently with the in-flight analyses.

Closed-loop water recycle systems for future manned space mission will required sensitive analytical methods to determine the quality of the water and insure the health and safety of the crew. As part of a NASA-funded study, we have been investigating techniques for the measurement of Total Organic Carbon (TOC) in water for use on the Space Station. The prototype system developed employs a membrane-based conductometric CO2 sensor which provides a gravity-independent means for measuring the amount of CO2 produced from the oxidation of organic compounds. Recently, we have been developing a system for the oxidation of organic compounds that does not require the use of chemical oxidizing agents. The reagentless oxidation reactor uses a combination of electrolytic and photolytic oxidation to convert organic compounds to CO2.

The development of a high sensitivity, compact monitor for the measurement of total organic carbon (TOC) in water with no gravity-dependent components is discussed. The system is based on a combination of photo-catalzyed oxidation of organic compounds to form carbon dioxide, which is selectively measured using a gas permeable membrane and conductometric detection. This unique combination permits the development of a TOC analyzer with significant advantages over existing methods for TOC analysis including high sensitivity (i.e., detection limits at low parts per billion TOC concentrations), a linear response over a wide range of TOC concentrations (at least four orders of magnitude), long-term stable calibration, compact design, and performance with minimal maintenance for semi-continuous and continuous monitoring capabilities. The results from our preliminary investigations on the development of the TOC monitor are presented.