The phenol-sulfuric acid method estimates carbohydrates by measuring the colour change that occurs when carbohydrates are dehydrated and react with phenol and sulfuric acid to produce a yellow-orange complex.
The phenol-sulfuric acid method is a colorimetric method for estimating the concentration of carbohydrates in a solution. It is based on the reaction between carbohydrates and phenol in the presence of concentrated sulfuric acid, which produces a yellow-orange to red-orange color complex.
The mechanism of the reaction is as follows:
Depolymerization of carbohydrates: The concentrated sulfuric acid breaks down the glycosidic bonds in carbohydrates, releasing monosaccharides.
Dehydration of monosaccharides: The monosaccharides are dehydrated to form furfural derivatives, such as 5-hydroxymethylfurfural (HMF) and furfural.
Reaction with phenol: HMF and furfural react with phenol in the presence of sulfuric acid to form colored complexes.
Question
What is the principle of carbohydrate estimation by phenol-sulfuric acid method?