What is Ellman’s reagent

Ellman’s reagent, also known as 5,5'-dithio-bis-(2-nitrobenzoic acid) or DTNB, is a water-soluble chemical commonly used to quantify free sulfhydryl groups (-SH). When added to a sample solution, Ellman’s reagent will react with free sulfhydryl groups to yield a yellow-colored product that can be measured using a spectrophotometer at 412 nm. The concentration of sulfhydryl groups within the test sample can then be estimated by comparison to a standard curve of known concentrations of sulfhydryl groups (e.g. cysteine). Ellman’s reagent has been used to quantify free sulfhydryl groups on proteins, peptides or tissues, as well as, to assess acetylcholinesterase activity.