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5,5′-Dithiobis(2-nitrobenzoic acid)

≥98%, BioReagent, suitable for determination of sulfhydryl groups

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3-Carboxy-4-nitrophenyl disulfide, 6,6′-Dinitro-3,3′-dithiodibenzoic acid, Bis(3-carboxy-4-nitrophenyl) disulfide, DTNB, Ellman’s Reagent
Linear Formula:
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Quality Level






240-245 °C (dec.) (lit.)


suitable for determination of sulfhydryl groups

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General description

5,5′-Dithiobis(2-nitrobenzoic acid) is also called DTNB or Ellman′s reagent. It is a water soluble reagent, which interacts with thiol groups, and can be used conveniently at neutral pH. Thiolate anion (RS-) reacts with Ellman′s reagent (DTNB2-), to produce 2-nitro-5-thiobenzoate anion (TNB2-) and one mixed disulfide (R-S-TNB-). TNB2- has a high molar absorption coefficient, and absorbs at 412nm. This absorption is independent of pH, at pH> 7.3.


Ellman′s reagent maybe used for acetylcholinesterase assay, and to specifically label cysteine residues. It is a sensitive reagent for measuring the free sulfhydryl content in proteins, peptides, and tissues.

Storage Class Code

11 - Combustible Solids



Flash Point(F)

Not applicable

Flash Point(C)

Not applicable

Personal Protective Equipment

dust mask type N95 (US), Eyeshields, Gloves

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Christian K Riener et al.
Analytical and bioanalytical chemistry, 373(4-5), 266-276 (2002-07-12)
Since its introduction in 1959, Ellman's reagent (5,5'-dithio-bis(2-nitrobenzoic acid)) has been the favorite reagent for spectrophotometric measurement of protein sulfhydryls. Meanwhile however, evidence has accumulated that many protein sulfhydryls give an incomplete reaction with Ellman's reagent, even during prolonged assay
Reassessment of Ellman's reagent.
P W Riddles et al.
Methods in enzymology, 91, 49-60 (1983-01-01)
Venkaiah Betapudi et al.
Science translational medicine, 12(527) (2020-01-24)
Chemical warfare nerve agents are organophosphorus chemical compounds that induce cholinergic crisis, leaving little or no time for medical intervention to prevent death. The current chemical treatment regimen may prevent death but does not prevent postexposure complications such as brain
Ellman's reagent: 5,5'-dithiobis(2-nitrobenzoic acid)--a reexamination.
P W Riddles et al.
Analytical biochemistry, 94(1), 75-81 (1979-04-01)
María Elena Quintanilla et al.
Frontiers in behavioral neuroscience, 14, 122-122 (2020-08-28)
Chronic ethanol intake results in brain oxidative stress and neuroinflammation, which have been postulated to perpetuate alcohol intake and to induce alcohol relapse. The present study assessed the mechanisms involved in the inhibition of: (i) oxidative stress; (ii) neuroinflammation; and


To measure chloramphenicol acetyltransferase activity, this procedure uses DTNB and coenzyme A. The reaction of DTNB with the –SH group on CoA results in a colorimetric increase at 412 nm.

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