2,2-diphenyl-1-picrylhydrazyl [ 1,1-DPPH,1,1-diphenyl-2-picrylhydrazil,1,1-diphenyl-2-picrylhydrazyl,2,2'-diphenyl-1-picrylhydrazyl,DPPH cpd,DPPH-1,1,alpha,alpha-diphenyl-beta-picrylhydrazyl,diphenyl-p-picrylhydrazyl ] A diphenyl picrate; the ability to decolorize this stable radical indicates reactivity of tested compounds (Banda, Anal Chem 46:1772-7 1974)