DETERMINATION OF HYDROCARBONS IN WATER BY EVANESCENT-WAVE ABSORPTION-SPECTROSCOPY IN THE NEAR-INFRARED REGION

An home-made EFA (evanescent field absorbance)-sensor has been tested for the determination of hydrocarbons in water. The investigations hav e been performed both with crude oil emulsions and petrol solutions, C uvette and evanescent wave spectra of crude oil and petrol in the near -infrared region are presented and discussed. The concentration of aro matic compounds in crude oil can be determined semiquantitatively by t he standard addition method. The sorption behaviour of the hydrocarbon s in the cladding of the fiberoptic sensor has been investigated and a correlation between the sensor signal and the concentration of the aq ueous hydrocarbon emulsion/solution could be shown, The desorption of the enriched molecules after the measurements is also presented. The p etrol molecules evaporate in ambient air so that the sensor is easily regenerated. In case of oil measurements the hydrocarbon molecules can not be removed by rinsing the sensor with clear water or by evaporatin g them in ambient air. It has to be regenerated by washing it with a h igh volatile solvent instead.