Purity >95%. DPPH, known formally as 2,2-diphenyl-1-picrylhydrazyl, is a cell-permeable, stable free radical that is commonly used to evaluate the ability of compounds to act as free radical scavengers or hydrogen donors and to measure the antioxidant activity of tissue extracts. The reaction of DPPH with an antioxidant or reducing compound produces the corresponding hydrazine DPPH2, which can be followed by color change from purple (absorbance at 515-528 nm) to yellow. The details and limitations of analysis have been recently reviewed.