Folin-Ciocalteau Reagent for Polyphenolic Assay

The Folin-Ciocalteau (F-C) method of assay is the simplest method available for the measurement of phenolic content in products. It is a development of Folin Denis reagent used in the early 19th century for the determination of tyrosine in proteins F-C reagent can be prepared by dissolving 100 g sodium tungstate (VI) dihydrate and 25 g sodium molybdate (VI) dihydrate with 700 ml distilled water, 100 ml concentrated hydrochloric acid, and 50 ml of 85% phosphoric acid to which is added 150 g of lithium sulphate hydrate. This reagent is very stable if protected from reductants and even when diluted if protected from light. For many years now, the F-C method of assay has been in use as a measure of polyphenol in natural products, and the basic mechanism is an oxidation/ reduction reaction with the phenolic group being oxidized and the metal ion reduced.