A reproducible, rapid and inexpensive Folin–Ciocalteu micro-method in determining phenolics of plant methanol extracts

A new combination among time, temperature, alkali and alcohol is described for the spectrophotometric determination of small concentrations of phenolics in methanol extracts from plant. It is a variation of the classical Folin–Ciocalteu (F–C) method, but the reaction conditions are optimized in order to eliminate methanol interferences in the assay. Alcohol concentration and reaction time limits have been evaluated as 4% methanol (v/v) and 20 min at 40 °C, using a 5% (w/v) sodium carbonate solution. This F–C micro-method is reproducible, quick, inexpensive and particularly helpful if it works with numerous samples or on a small scale, such as during the setting up of an experimental procedure of alcoholic extractions.