<title>Quantitative analysis of aromatic molecules in water by laser-induced fluorescence spectroscopy and multivariate calibration techniques</title>

Abstract

We introduce a fiber optical sensor which is capable of analyzing polycyclic aromatic hydrocarbons (PAHs) and monoaromatics like benzene, toluene, xylene, and ethylbenzene (BTXE) in natural water samples. The compact system is based on laser-induced, time-resolved fluorescence emission spectroscopy. It uses a miniaturized all solid state laser which can be operated at 266 nm and 355 nm. The 3-D data set of a time-resolved fluorescence spectrum is reduced to a 2-D data set by a factor based technique, i.e. by dividing the raw data by a decay matrix with exponential decay profiles. The resulting data have a 2-D spectral format but still contain the temporal information. With these data a partial least squares regression has been carried out and optimized for a quantitative evaluation of the data. After the calibration xylene could be selectively analyzed in the 0 - 200 ppb range with a prediction error of 15 ppb. The PAH calibration was able to predict the concentration of 9 out of 15 EPA PAHs with errors between 0.07 (mu) g/l (benzo[a]pyrene) and 1.6 (mu) g/l (anthracene, naphthalene).