Detection of aromatic hydrocarbons with infrared evanescent-wave fiber optic sensors

This paper describes initial studies that were performed to develop a personal wear badge for the accumulated exposure detection of benzene vapor. Small sections of optical fiber were coated with a membrane specific for the adsorption of benzene vapor. After exposure the fiber was placed in a Fourier transform infrared (FTIR) spectrometer and the infrared spectra of the surface bound benzene was obtained. The qualitative exposure levels were determined by peak intensities. Benzene was detected at a concentration of 100,000 ppm. Dichlorobenzene was also detectable (80,000 ppm) and could be differentiated from benzene by unique absorbance peaks. The sensor was reusable and the cumulative exposure was determined as a function of time. The sensor modifications were based on the incorporation of benzene absorbing compounds contained in a thin, high surface area porous membrane coating applied to the fiber surface. The surface coating technology was developed and demonstrated on an active fiber system. A sensor cell was designed to allow handling and direct insertion into the FTIR spectrometer.