Spectrophotometric microdeterminations of aldoses with p-amino-benzoic acid

Abstract

Aldoses, neutral and acidic (10–120 µg.), and glucosamine in larger amounts, can be measured spectrophotometrically at 370 mµ after heating in acetic acid with p-aminobenzoic acid. When sulphosalicyclic acid is included in the reagent, pentoses and hexuronic acids show two marked λ_max. at 370 and 540 mµ; hexoses also show a small extinction at 540 as well as a large one at 370 mµ. At both wavelengths the four pentoses show the same proportionalities between extinction and concentration. Glucose, galactose, and mannose behave similarly; as their proportionalities are distinct from those of the pentoses, it is practicable to analyse mixtures of total hexose and total pentose. Rhamnose and fucose have a high extinction at 370 but do not absorb at 540 mµ.

The absorption spectra shown by reactions of the sugars with the two reagents are different. Without added sulphosalicylic acid, all classes of sugar examined gave very similar curves, indicating a possible initial reaction between the reducing group and the arylamine. In presence of sulphosalicylic acid the curves closely resembled those obtained by treating the appropriate furfuraldehyde.

The method is flexible and may be scaled up or down, and can be used in presence of inert organic solvents. Interference by non-carbohydrates is confined to thiols and large amounts of tryptophan, of ten substances tested.