ANALYSIS OF POLYNUCLEAR AROMATIC-COMPOUNDS USING LASER-EXCITED SYNCHRONOUS FLUORESCENCE

Monitoring the presence and distribution of polynuclear aromatic compo unds (PACs) in the environment is an important task due to the presenc e of these species in many types of environmental samples. Molecular f luorescence is often used for this task, usually after extensive sampl e cleanup and separation, due to the speed and the inherent sensitivit y of the technique for PACs. When synchronous fluorescence is used for PAC analysis, the amount of sample pretreatment can often be reduced due to the greater selectivity of the technique relative to convention al fluorescence emission. Another method of increasing sensitivity and selectivity is to use lasers as the excitation source in molecular fl uorescence. An added advantage of lasers is the high source coupling a nd fluorescence collection efficiencies when fiber optics are used for remote sensing applications. In this work, the applicability of laser -excited synchronous fluorescence for the analysis of PAC mixtures is evaluated. A prototype laser-excited synchronous luminescence (LSL) in strument has been previously determined to offer significant advantage s over conventional laser-excited fluorescence [C.L. Stevenson and T. Vo-Dinh, Appl. Spectrosc., 47 (1993) 430]. An improved version of the LSL instrument is presented here with superior scanning precision and extended wavelength scanning range. In addition to demonstrating the c apabilities of the improved LSL instrument for mixture analysis, the s ensitivity of this improved instrument is compared to that of a commer cial fluorimeter. Finally, the capability of the LSL instrument to fur ther improve selectivity using time-resolved synchronous fluorescence is illustrated.