EVANESCENT FIBER OPTIC CHEMICAL SENSOR FOR MONITORING VOLATILE ORGANIC-COMPOUNDS IN WATER

The transport of trichloroethylene, 1,1,1-trichloroethane, and toluene in aqueous solutions through a polydimethylsiloxane film was modeled using a Fickian diffusion model to fit data obtained from an evanescen t fiber-optic chemical sensor (EFOCS). The resultant diffusion coeffic ients for these analytes were respectively 3 x 10(-7), 5 x 10(-7), and 1 x 10(-7) cm(2)/s. Inclusion of an interfacial conductance term, def ined as the ratio of the mass transport coefficient across the polymer surface and the analyte diffusion coefficient in the polymer, was req uired to accurately model the data. It was determined that the interfa cial conductance terms were generally of the same order of magnitude f or the analytes examined, suggesting a constant transport mechanism fo r the analytes. Linear chemometric algorithms were used to model the E FOCS response to aqueous mixtures of the three analytes with individua l analyte concentrations between 20 and 300 ppm. Both partial least-sq uares and principal component regression algorithms performed comparab ly on the calibration sets, with cross-validated root-mean-squared err ors of prediction for trichloroethylene, 1,1,1-trichloroethane, and to luene of approximately 26, 29, and 22 ppm, respectively. The resultant prediction model was then used to determine analyte concentrations in an independent data set with comparable precision.