FIELD EXPERIMENTS WITH A PORTABLE FIBEROPTIC SENSOR SYSTEM FOR MONITORING HYDROCARBONS IN WATER

The prototype of a portable fiber-optic sensor system for monitoring a polar hydrocarbons in groundwater or industrial wastewater is presente d, This sensor system can be used for quantitative in situ analysis of organic pollutants like chlorinated hydrocarbons, aromatic hydrocarbo ns, or fuels in a broad concentration range from around 200 mu g I-1 u p to a few 100 mg I-1. The sensing principle is based on the reversibl e enrichment of analyte molecules in a hydrophobic silicone cladding o f a quartz glass optical fiber and the direct (spectro)photometric mea surement of the extracted species in the polymer through the evanescen t wave, The sensing fiber of 12-30-m length is coiled to a compact, cy lindrical geometry (14 x 5 cm in size) on a stainless steel support an d can be connected via all-silica fibers with a length of up to 100 m to a low-cost bandpass filter photometer developed at the IFIA, thus a llowing even remote analysis, This instrument provides a sum concentra tion signal of the extracted organic compounds by measuring the integr al absorption at the C-H overtone bands in the near-infrared spectral range, Field measurements with the sensor system have been performed a t the research facility for subsurface remediation VEGAS of the Unrive rsitat Stuttgart, and at a former chemical landfill in Muhlacker, Germ any, These in situ experiments were carried out in water mainly contam inated with chlorinated hydrocarbon compounds. A comparison of the in situ data and laboratory reference analyses of aqueous samples drawn d iscontinuously gave rather satisfactory agreement between both data se ts with a mean deviation of 9% for the VEGAS experiments and 20% for t he Muhlacker field trials, (C) 1998 John Wiley & Sons, Inc.