Folin-Ciocalteu reagent

The Folin-Ciocalteu reagent or Folin's phenol reagent is a mixture of phosphomolybdate and phosphotungstate used for the colorimetric assay of phenolic antioxidants and polyphenol antioxidants. It works by measuring the amount of the substance being tested needed to inhibit the oxidation of the reagent. This reagent forms part of the Lowry protein assay and will also react with some nitrogen-containing compounds such as hydroxylamine and guanidine.

This reagent should not be confused with Folin's reagent, which is used to detect amines and sulfur-containing compounds.