text: The Folin–Ciocâlteu reagent (FCR) or Folins phenol reagent or Folin–Denis reagent, is a mixture of phosphomolybdate  and phosphotungstate used for the colorimetric in vitro' assay of phenolic and polyphenolic antioxidants, also called the gallic acid equivalence method (GAE).  It is named after Otto Folin, Vintilă Ciocâlteu, and Willey Glover Denis. The Folin-Denis reagent is prepared by mixing sodium tungstate and phosphomolybdic acid in phosphoric acid. The Folin–Ciocalteu reagent is just a modification of the Folin-Denis reagent. The modification consisted of the addition of lithium sulfate and bromine to the phosphotungstic-phosphomolybdic reagent.
  The reagent does not measure only phenols, but will react with any reducing substance. It therefore measures the total reducing capacity of a sample, not just phenolic compounds. This reagent is part of the Lowry protein assay, and will also react with some nitrogen-containing compounds such as hydroxylamine and guanidine. The reagent has also been shown to be reactive towards thiols, many vitamins, the nucleotide base guanine, the trioses glyceraldehyde and dihydroxyacetone, and some inorganic ions. Copper complexation increases the reactivity of phenols towards this reagent.
  This reagent is distinct from Folin's reagent, which is used to detect amines and sulfur-containing compounds.
  A 1951 paper entitled "Protein measurement with the Folin phenol reagent" was the most cited paper in the 1945–1988 Science Citation Index, with 187,652 citations.