Fluorescence excitation-emission matrix measurement and analysis of groundwater contaminants

A fluorescence excitation-emission matrix (EEM) measurement system is described which employs laser excitation and optical fiber delivery for remote sensing applications. Ultraviolet light is generated at a variety of discrete wavelengths by pumping a Raman shifter with the third and fourth harmonics of a Nd:YAG laser, and this Raman-shifted light is used for fluorescence excitation to generate EEM spectra. Optical fibers are used for laser beam delivery and fluorescence data collection, and a diode array detector is used to detect fluorescence emission spectra. To test the capability of this instrument, the composition of a 3-component mixture of phenol, dibenzofuran and 2-naphthol and a 4-component mixture of m-cresol, p-cresol, carbaryl and carbofuran is determined quantitatively. Detection limits were in sub-ppb range.;Quantitative analysis of the laser-induced fluorescence (LIF) EEM data obtained from this instrument is done by two methods. First one is a least squares method. Quantitative information can be obtained from fluorescent mixtures using method of least squares based on previously determined calibrated excitation-emission matrices of known components even in cases of severe overlap. The least squares method is found satisfactory for analysis of three different mixtures of groundwater pollutants if all components were known.;A second scheme for quantitative analysis of a multicomponent fluorescent mixture using Excitation-Emission Matrix (EEM) has also been tested. This method, rank annihilation, is capable of quantifying a particular component known to be present without having also to know the identity of the rest of the components. The theory of the method and the results of its application to 3 mixture matrices are presented and comparison is made with the method of least squares.;A multichannel fluorescence EEM detector has been developed for use in high-performance liquid chromatography (HPLC). An array of different color laser beams throughout the deep UV region of the spectrum are created simultaneously by pumping a Raman shifter with 266 nm light from a Nd:YAG laser. Ten of these laser beams are launched into an array of optical fibers that transport the light to an HPLC detection cell. Laser-excited fluorescence emitted from eluents is carried by a separate set of optical fibers to a CCD based detection system that detects all the channels simultaneously in real time (1 second per exposure). LIF-EEM chromatographic peak widths are comparable to peak widths obtained with a commercial 8;Dependence of matrix size on the accuracy of the quantitative analysis of the fluorescence excitation-emission matrices (EEMs) is evaluated. Fluorescence emission and excitation spectra of benzene, naphthalene and anthracene with known concentrations are collected using a conventional fluorimeter and their EEMs (with various matrix sizes) are generated. An EEM of a mixture solution of these three compounds is also obtained and this EEM is truncated to generate EEMs of various matrix sizes. Quantitative analysis of the mixture EEMs is done using the method of least squares and the results are compared. Similar experiment is done with a mixture of benzene, toluene, ethylbenzene and p-xylene and the results are compared.