This practice is useful for detecting and identifying (or determining the absence of) 90 chemicals with relatively high fluorescence yields (see Table 1). Most commonly, this practice will be useful for distinguishing single fluorescent chemicals in solution, simple mixtures or single fluorescing chemicals in the presence of other nonfluorescing chemicals. Chemicals with high fluorescence yields tend to have aromatic rings, some heterocyclic rings or extended conjugated double-bond systems. Typical chemicals included on this list include aromatics, substituted aromatics such as phenols, polycyclic aromatic hydrocarbons (PAH's), some pesticides such as DDT, polychlorinated biphenyls (PCB's), some heterocyclics, and some esters, organic acids, and ketones.

TABLE 1 Summary of Experimental Parameters and Results

With appropriate separatory techniques (HPLC, TLC, and column chromatography) and in some cases, special detection techniques (OMA's and diode arrays), this practice can be used to determine these 90 chemicals even in complex mixtures containing a number of other fluorescing chemicals. With the use of appropriate excitation and emission wavelengths and prior generation of calibration curves, this practice could be used for quantitation of these chemicals over a broad linear range.

Fluorescence is appropriately a trace technique and at higher concentrations (greater than 10 to 100 ppm) spectral distortions usually due to self-absorption, or inner-filter effects but sometimes ascribed to fluorescence quenching, may be observed. These effects can usually be eliminated by diluting the solution. Detection limits can be lowered following identification by using broader slit widths, but this may result in spectral broadening and distortion.

This practice assumes the use of a corrected spectrofluorometer (that is, one capable of producing corrected fluorescence spectra). On an uncorrected instrument, peak shifts and spectral distortions and changes in peak ratios may be noted. An uncorrected spectrofluorometer can also be used if appropriate data is generated on the instrument to be used.