66 SPIE Proceedings of the symposium on Chemical, Biochemical, and Environmental Fiber Sensors X, November 1998, SPIE volume 3540, pp. 66-74. FTIR Based Instrument Employing a Coiled Hollow Waveguide Cell for Rapid Field Analysis of Volatile Organic Compounds R. H. Micheels a , K. Richardson a , D. J. Haan b and J. A. Harrington b a Polestar Technologies, Inc., 220 Reservoir St., Suite 32, Needham Heights, MA 02494 b Fiber Optics Materials Research Program, Rutgers University, 607 Taylor Rd., Piscataway, NJ 08854-8605 ABSTRACT An instrument has been developed which combines a portable Fourier Transform Infrared (FTIR) spectrometer with a hollow waveguide infrared gas cell. This instrument has been applied to the multi-component analysis of 5 volatile organic compounds (VOCs), that are common contaminants in soil. The instrument is designed for rapid field screening of these VOC compounds in soil or water. The instrument employs headspace sampling in small sample vials to measure the VOC content of soil or water samples. The instrument employs either a straight or coiled hollow waveguide gas cell to achieve a long infrared absorption pathlength of 1 – 2 m with a very low cell volume in the range of 2 to 5 cc. These cell dimensions permit high detection sensitivity along with a rapid system response time. A theoretical model has been developed to predict the infrared light attenuation in the coiled waveguide cell as a function of coil radius and waveguide bore size. Incoherent infrared light transmission losses associated with coiling of waveguides with a 0.197 m coil radius have been found to have an average value of 0.312 dB/m. Calibration experiments have been performed with a series of 5 component VOC gas mixtures with concentrations in the range of 20 – 200 ppm (volume). Measurements of the partitioning of the VOCs between the soil and gas phase have also been conducted. Keywords: infrared spectroscopy, FTIR, VOCs, hollow waveguide 1. INTRODUCTION There is a need to develop improved field portable instrumentation for rapid analysis of soil and water samples for trace amounts of volatile organic compounds (VOCs) in screening of toxic waste sites. These VOC compounds can originate from organic solvents used for cleaning or processing and from fuels derived from petroleum. At present there are two types of commercially available instruments that have been used for site screening which have the capability of both identification and quantitative analysis of a wide range of VOCs: portable gas chromatographs (GC) and portable gas chromatograph/mass spectrometers (GC/MS) 1 . These two types of instruments are limited by slow measurement cycle times, typically greater than 10 min. per sample 2 . Portable GC instruments normally employ only a single column which is not sufficient to provide unambiguous identification of all commonly occurring VOCs because of co-elution of some compounds. Portable GC/MS instruments have extensive maintenance requirements. A new instrumental approach that has been developed for field analysis of VOCs in soil and water samples is based on headspace sampling using a portable Fourier Transform infrared (FTIR) spectrometer combined with a low volume hollow waveguide gas cell. This new approach permits a fast analysis cycle time of about 1 min. and requires very little maintenance. In this study, the FTIR/hollow waveguide approach has been applied to the analysis of the 4 BTEX compounds: benzene, toluene, ethylbenzene, and xylenes; and trichloroethylene. Infrared transmitting hollow waveguides which employ a two layer metal/dielectric reflective coating, have been developed within the last 10 years and have primarily been used for flexible infrared laser beam delivery for surgical