Time-resolved laser-excited phosphorimetry is proposed for the direct analysis of 2,3,7,8-tetrachloro-dibenzo-para-dioxin in complex mixtures at 4.2 K. Measurements are easily made with the aid of a cryogenic fiber-optic probe, which provides excellent precision of measurements and high quality spectra. A tunable dye laser with a narrow bandwidth allows selective excitation in mixtures with highly overlapped excitation spectra. The selectivity of analysis is further enhanced with time-resolution of both fluorescence and phosphorescence interference. Detection at the parts-per-billion level (ng·mL<sup>-1</sup>) is made with the aid of photon counting. Our results demonstrate the feasibility of detecting 2,3,7,8-tetrachloro-dibenzo-para-dioxin in the presence of dioxin isomers and other organic pollutants such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and polychlorinated dibenzofurans. Because of the selectivity of our approach, it was possible to spectroscopically resolve mixtures containing up to 43 components.

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