DTNB; Ellman's Reagent, 5,5'-Dithiobis-(2-Nitrobenzoic Acid)

DTNB or Elman's reagent can be used to quantitate thiols in proteins, cells and plasma by absorption measurements. It readily forms a mixed disulfide with thiols, liberating the chromophore 5-merapto-2-nitrobenzoic acid (absorption maximum 410 nm). Only protein thiols that are accessible to this water-soluble reagent are modified.