DTNB is known as Ellman’s reagent. It is used for the colorimetric determination of thiol groups in biological samples. It is fairly soluble in water. Colorless DTNB is converted to yellow 5-Mercapto-2- nitrobenzoic acid in the presence of thiol compounds (Fig. 1). As 5-Mercapto-2-nitrobenzoic acid has an absorption maximum at 412 nm, the absorption spectrum of DTNB does not interfere with thiol detection (Fig. 2).
Fig. 1 DTNB reaction with thiol compound
Fig. 2 Absorption spectra of DTNB and reduced DTNB
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