Figure 1: Each Aroclor formulation (e.g. Aroclor 1254, Aroclor 1242) has a different pattern of peaks. As the percent chlorine increases or decreases, the pattern is shifted right or left. A) GC-ECD chromatograms are instrument recorded peaks that display the retention time vs instrument response. Image: Aroclors on Rtx-PCB, courtesy of www.restek.com. B) Histograms use the PCB congener number and reported concentration values to improve data visualization. Image: Tabulated congener distributions (weight %), using: FRAME, G. M. 1997. Fresenius J Anal Chem, 357, 701-713.