Fiber optic sensors using novel substrates for hydrogen sulfide determination by solid surface fluorescence

Two different fiber optic sensors were developed for the determination of h ydrogen sulfide at ppb concentration levels; a probe-type fiber optic senso r coated with polyethylene oxide containing 0.5 M CdCl2 and a fiber optic s ensor utilizing 0.5 M CdCl2-pretreated filter paper as solid substrate. In the first type, CdCl2-polyethyleneoxide (PEO) mixture was coated onto the t ip of a fiber optic probe and the probe was exposed to H2S. The methodology is based on the measurement of CdS fluorescence on the surface. Detection limit (3s) of the PEG-coated fiber optic system was 36.0 ppb for H2S and pr ecision at the 0.552 ppm level was 29% R.S.D. For the fiber optic system ut ilizing CdCl2-pretreated filter paper, two different configurations were de vised and evaluated; a bifurcated fiber optic sensor and a single fiber opt ic sensor. Similar figures were obtained with these two systems; the detect ion limit (3s) was 4.0 ppb for the bifurcated fiber optic sensor and 4.3 pp b for the single fiber optic sensor, and both sensors had linear responses in the range 0.032-1.0 ppm. Their precisions at 0.299 ppm level were also v ery similar, 10 and 11% R.S.D., respectively, for the bifurcated and single fiber systems. In addition to the tiber optic sensors developed, various s urfactants (sodiumdodecylsulfate (SDS), Aerosol OT, Aerosol A102, Aerosol 5 01), some cellulosic substances (sodium carboxymethylcellulose (CMC), ethyl cellulose, hydroxypropylmethylcellulose! ethylhydroxyethylcellulose, cc-cel lulose) and several water-soluble polymers (polyacrylicacid polyethleneoxid e (PEO), polyvinylalcohol (PVA)) were dissolved in proper solvents and afte r mixing with 0.5 M CdCl2, were spread over glass slides. These novel solid substrates were exposed to H2S and fluorescence signal on the surfaces of the glass slides was measured with a luminescence spectrometer. The new sub strates were shown to be good alternatives to filter paper for the determin ation of H2S by room temperature solid surface fluorescence spectrometry. ( C) 2000 Elsevier Science B.V. All rights reserved.