Ammonium Metavanadate as a Reagent for Reducing Carbohydrates.

Abstract

A reagent consisting of 2% ammonium metavanadate in 10% sodium carbonate solution has proved effective in the detection of reducing carbohydrates or of non-reducing carbohydrates after hydrolysis. To make a test we heat on the water-bath 2 cc. of a 0.25% or 0.50% solution of the compound under consideration with 5 cc. of the reagent. A brownish to yellow color develops with a slight precipitate. On the addition of 1% hydrochloric acid, the mixture becomes clear and assumes a characteristic green color, due to the reduction of the metavanadate to a compound in which vanadium holds a lower valence. The acid must be added in quantities just sufficient to neutralize the reaction mixture, the point of neutralization being determined with litmus paper. The following compounds reduced with the formation of the characteristic color: pentoses (xylose, arabinose, rhamnose); hexoses (glucose, glucosamine, levulose, galactose, mannose); disaccharides (lactose, maltose, cellobiose). The following compounds reduced only after preliminary subjection to hydrolysis followed by neutralization: disaccharides (sucrose, trehalose); trisaccharides (raffinose, melizitose); polysaccharides (dextrin, starch, inulin, glycogen, cellulose); glucosides (aesculin, amygdalin, arbutin, phloridzin, strophantin, picrotoxin, salicin, saponin); gums (arabic, acacia, tragacanth); glycoproteins (mucin, ovomucoid); glycolipins (phrenosin); nucleic acid. Compounds other than carbohydrates also reduced. Cysteine gave a green color; lactic acid, a royal blue; oxalic acid, a green; mucic acid and citric acid, dark blue; tartaric acid, a royal blue with a purplish tinge; and pyruvic acid, green. The reagent, however, is more sensitive to the sugars than to the organic acids. The limit of sensitivity for glucose is 0.03%. Citric acid reduces in a 3% solution, but not in a 2% solution. Tartaric acid reduces in a 2% solution, but not in a 1% solution. Lactic acid does not react in a 0.9% solution.