---
title: "Ellman's reagent: research glossary | Sable Peptides"
description: "Ellman's reagent, 5,5'-dithiobis(2-nitrobenzoic acid) or DTNB, reacts with free thiol groups to release a yellow product that absorbs at 412 nm. It is used"
canonical: https://www.sablepeptides.co.uk/glossary/ellman-s-reagent
publisher: Sable Peptides Limited (UK company 17488610)
note: Research use only. Not for human or veterinary use.
---

Glossary

# Ellman's reagent

Ellman's reagent, 5,5'-dithiobis(2-nitrobenzoic acid) or DTNB, reacts with free thiol groups to release a yellow product that absorbs at 412 nm. It is used to quantify free cysteine thiols in peptides, for example to confirm complete disulfide formation or the availability of thiols for conjugation.

Source: [en.wikipedia.org](https://en.wikipedia.org/wiki/Ellman's_reagent)

## Related terms

-   [Cysteine](/glossary/cysteine)
-   [Conjugation](/glossary/conjugation)

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