All poiychlorlnated dlbenzo-p-dioxln (PCDD) Isomers containing four and more chlorine substituents were prepared by mlcropyrolysls of chlorophenates. The syntheses included the preparation of all 22 tetra-, 14 penta-, 10 hexa-, 2 hepta-, and octachiorinated species (tetra-to octa-CDD). The gas chromatographlc and mass spectrometrlc properties of these Isomers were studled. Hlgh-resoiutlon gas chromatography (HRGC) on a 55-m Sllar 1Oc ...