Methane hydrates formed in deep sea and permafrost areas are ice-like solids composed of water and large amounts of methane. Research efforts are aimed to understand their potential role as a major energy resource in the future. Furthermore, thorough investigations of methane hydrates are required to understand their impact on the environment and potential off-shore drilling hazards. However, the oceanic environments enabling the existence of methane hydrates are not readily accessible to long-term, in-situ analyses. IR-ATR spectroscopy has been established as a technique for in-situ monitoring of organics in harsh, aquatic environments. Investigations using this principle utilize silver halide fibers with polymer coatings to enrich hydrophobic analytes, protect the waveguide, and minimize the IR background absorbance of water. Hydrophobic analytes present in the polymeric enrichment layer interact with the evanescent field as light propagates through the fiber producing a readily measurable signal. These principles are currently being extended for the development of a sensor system capable of performing in-situ investigations of dissolved methane in seawater as part of an interdisciplinary research effort for monitoring methane hydrates in the Gulf of Mexico. As a first step towards an ATR FT-IR sensor system capable of measuring methane in water, tetrachloroethylene was used as a model analyte to determine enrichment times into various polymer membranes. Various concentrations of tetrachloroethylene were enriched into a Teflon AF 1601® (DuPont) membrane. Linear calibrations were obtained with T90 times in the region of 15 minutes. Measurements were carried out to evaluate the dependence of enrichment times on the flow rate indicating that lower flow rates lead to longer T90 values. In a next step, the enrichment behavior of tetrachloroethylene into the highly permeable membrane poly(trimethylsilyl)propyne is investigated. Future work will focus on establishing a polymer library suitable for measuring dissolved methane, as well as other analytes.
Back to Chemical Sensors: New Frontiers (General Session)
Back to The 56th Southeast Regional Meeting 2004 (November 10-13, 2004)