Determination of soluble carbohydrates from the absorbances of sulphonated 1-naphthol derivatives of hexoses and pentoses.

Abstract

A modified Molisch test was used in quantitative spectrophotometric analyses for glucose and xylose in mixed solutions. The algebraic method for determination of substances exhibiting additive absorbances was found to apply to these mixtures. The two wavelengths at which the most reliable measurements were obtained were 530 and 580 mμ. An isosbestic point was found at 562.7 mμ at which the glucose–xylose ratio had no effect on the absorptivity, thus allowing a measurement of the sum of the concentrations of the two sugars.This method of analysis was used to determine the concentrations of hexoses and pentoses in acid extracts of forages and feces from sheep fed these forages in digestibility experiments. The carbohydrates detected by this method of analysis had a greater digestibility than is usual for the conventional nitrogen-free extracts. The digestibilities of hexoses and pentoses extracted from several forages averaged 87 and 70%, respectively. The levels of uronic acids in the extracts were found to be below the level of appreciable interference with the measurements of the monosaccharides.