2003 Volume 13 Issue 3 Pages 705-718
Photodegradation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in the analytical process was studied.
Firstly, photolysis patterns of 4-8 chlorinated congeners of PCDDs/PCDFs substituted with chlorine atoms at the lateral (2, 3, 7 and 8) positions (2, 3, 7, 8-PCDDs/PCDFs) were investigated in organic solvents by irradiation with UV 365 nm (UV intensity: 3, 000μW/cm2) in a glass test tube with a thickness of 1.2mm. PCDFs and 2, 3, 7, 8-TeCDD were found to be decomposed to reductive dechlorinated compounds (RDC) . In PCDFs, compounds substituted with chlorine at both 1 and 9 positions were rapidly decomposed, particularly 1, 2, 3, 7, 8, 9-HxCDF being decomposed the most quickly with a half-life in toluene of 35.6 minutes. These photodegradations were also observed by irradiation with fluorescent light (UV intensity: 100μW/cm2) in toluene with a half-life (1, 2, 3, 7, 8, 9-HxCDF) of 11 hours.
Secondly, influence of these photodegradations on the measurement by internal standard method was investigated. As a ratio of 12C-parent compound (analysis object) to 13C-parent compound (internal standard) differs from sample to sample, and decreased or increased amount of PCDDs/PCDFs can appear after photodegradation, their concentrations calculated by the internal standard method will be different from the original one. These views were confirmed by irradiation experiment to solutions with various concentrations of 12C PCDDs/PCDFs.
