OPTIMIZATION OF AN INTEGRATED OPTICAL EVANESCENT-WAVE ABSORBENCY SENSOR FOR THE DETERMINATION OF CHLORINATED HYDROCARBONS IN WATER

The suitability of an integrated optical chemical sensor for the deter mination of highly volatile chlorinated hydrocarbons in aqueous soluti ons has been proven. The analytes are detected by NIR absorption spect rometry in the evanescent field of an integrated optical strip wavegui de generated in a BGG31 (Schott, Germany) glass substrate, which is co ated with a hydrophobic polymer superstrate as sensing layer. It has b een shown that the sensitivity increases when the refractive index of the superstrate is increased from 1.333 up to 1.46. Different UV-cured polysiloxanes with low cross sensitivity to water have been prepared. Due to the good light transmission properties of the IO-sensors prepa red by this method, quantitative measurements have been performed with the model system trichloroethene (TCE) in water. A detection limit of 22 ppm has been found and the sensor response times (t(90)-value) are between five and fourteen minutes for a coating thickness of around 3 0 mu m. The sensor response is totally reversible. The analyte desorbe s in air within 2 min. The enrichment of trichloroethene in the polysi loxane coating can be described by film diffusion through the aqueous boundary layer as rate determining step.