Qualitative and quantitative colorimetric determination of heptoses.

All heptoses produce with orcinol in dilute HCl two characteristic colored compounds which differ greatly in their absorption spectra. Three different modifications of this reaction were found useful. Procedure i--To 2 cc. of a solution containing 20 to 100 y per cc. of ketoheptose or 5 times as much of an aldoheptose is added 0.4 cc. of concentrated HCl, sp. gr. 1.19, in a test-tube with a ground glass stopper, and the mixture is immersed for 1 hour in a boiling water bath. Then 0.4 cc. of a solution of 13 mg. of FeC13.6HzO in 100 cc. of 2 N HCl and 0.15 cc. of a 6 per cent solution of orcinol in ethanol are added to the sample. A blank containing water instead of the unknown is run simultaneously. The tube is submerged for exactly 3 minutes in a boiling water bath. A bluish purple color appears in the heptose solution. The solution is then diluted with an equal amount of distilled water. The color becomes a reddish purple. Procedure g-The bluish purple reaction mixture obtained after 3 minutes heating with orcinol is diluted with double its volume of either ethanol or glacial acetic acid. In this case the bluish purple color changes to greenish blue. If the mixture diluted with glacial acetic acid is further heated for 15 minutes in a boiling water bath, the intensity of the bluish green color increases. Procedure Z-The heptose solution (2 cc.) is heated and mixed with FeC13 as in Procedure 1; 4 cc. of glacial acetic acid and 0.15 cc. of 6