Polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) consist of 210 different compounds with varying degrees of toxicity, and the 17 congeners with chlorine substitution in the 2,3,7,8 positions are considered the most toxic. This chromatogram illustrates the separation of a 17 component 2,3,7,8-substituted PCDD and PCDF standard on a 30 m x 0.25 mm I.D. x 0.25 μm SLB-5ms column. Note the resolution between 1,2,3,4,7,8-HxCDD and 1,2,3,6,7,8-HxCDD. US EPA Method 8280, which is for the analysis of these compounds by low resolution GC-MS, requires ≥ 50% resolution between these two isomers.