A UV spectroscopic method for monitoring aromatic hydrocarbons dissolved in water

An enhanced UV spectrometric method is applied to trace measurements of aromatic hydrocarbons dissolved in water. This approach gains selectivity and sensitivity by the use of optically generated first and second derivatives of transmission spectra. The augmented spectroscopic technique is combined with chemometric algorithms like principal component regression or partial least asquares which are used for calibration of the spectrometer and quantitative evaluation of spectra. Laboratory measurements were performed on mixtures containing up to five substances, i.e. benzene, toluene, ethylbenzene, the three xylene isomers, chlorobenzene, and gasoline. Due to the difficulty of preparing precisely defined calibraation and test samples of these very volatile compounds, a novel mixing device was developed and is presented. From these first investigations it can be estimated that the detection limits are down to ca. 10 µg analyte per liter of water by using a 10 cm absorption pathlength and a few minutes measurement time.