A modified anthrone-sulfuric acid method for the determination of fructose in the presence of certain proteins.
Two milliliters of a reagent consisting of anthrone and tryptophan each at a 0.01% concentration in 75% sulfuric acid, when added to 0.9 ml of solution containing D-fructose, produced on heating (55 degrees C, 90 min) a pink color (lambdamax 520 nm) with an absorbance of 0.009 A/nmol. The absorbance is about three times higher than that of the standard anthrone-sulfuric acid reagent. Glucose yields a color only about 1% as intense as that yielded by fructose. The method is useful for the estimation of fructose in the presence of proteins. Synthetic Amadori compounds and glycosylated proteins containing ketoamine-linked fructose, however, were unreactive.