Benedict Test is method detect carbohydrate by using reducing properties of them. Some of the carbohydrates can reduce metals, in Benedict Test this metal is Copper, so color change could be observed.In reaction Copper +2 reduce to Copper+1 and resulting color change.
Benedict reagent composed from sodyum carbonate, that gives alkaline properties to solution, Cooper (2) Sulphate pentahydrate gives Copper +2 ions to solution and sodyum citrate complex with Copper to prevent further reactions.Alkaline properties can cause tautomerism in reducing sugar which result reaction.After adding carboydrates different color changes can be observed. Oxidized from of Copper gives brown reddish and copper +2 gives blue color in reaction. From Reddish brown to blue different color shows decreasing concentration of the carbohydrates. Only reducing sugars can give positive results, if carbohydrate do not have reducing property such as sucrose reagent remain blue, even though carbohydrate is present.(3*)
Phenol sulfuric acid method is coloration method that determine whether substance contain polysaccharide, disaccharides , monosaccharide or not.Sulfuric acid degrades those compounds and phenol complex with degraded particles and gives yellow color. After color change absorbance amount compared with standards so detection of carbohydrates by quantitative analysis is achieved.
In this laboratory difference between quantitative and qualitative analysis were investigated by comparing Phenol Sulfuric acid Method and Benedict Test results. Carbohydrate determination analysis were also investigated by using standard glucose and glycogen in Phenol Sulfuric acid method. Difference between reducing sugars and non reducing sugars were studied by using different samples in Benedict Test.(4*)