APPLICATION OF A 2-DIMENSIONAL CHROMATOGRAPHY SYSTEM FOR GAS-PHASE PHOTODEGRADATION STUDIES OF POLYCHLORINATED DIBENZO-P-DIOXINS

Gas-phase photodegradation of polychlorinated dibenzo-p-dioxins was st udied with a two-dimensional gas chromatographic system consisting of two independently operated gas chromatographs interfaced to a photorea ctor. Gas flow through the chromatographs and photoreactor were direct ed with two switching valves. This arrangement permitted isolation and irradiation of solute in the photoreactor for varied periods and unde r different atmospheres. The irradiation experiments revealed that dif ferent dioxin congeners degrade at different rates; e.g., a 20-min irr adiation resulted in the degradation of approximately 80% of 2,3,7-tri chlorodibenzo-p-dioxin, while only 30% of the 2,3,7,8-tetrachlorodiben zo-p-dioxin was found to degrade under the same conditions. As expecte d, photodegradation rates decreased with an increase in the number of chlorines. Degradation rates were also influenced by the position of c hlorine substitutions. The results showed that, in contrast to solutio n-phase studies, congeners with peri chlorines photodegrade more rapid ly than congeners with laterally substituted chlorines. These results indicate that, in the gas phase, more toxic (laterally substituted) co ngeners are more persistent than less toxic (peri substituted) analogu es.