A modified uronic acid carbazole reaction

A modification of Dische's carbazole reaction for uronic acid in the presence of borate is described. The advantages of the procedure are: (1) There is an approximately twofold increase of sensitivity. The OD is a linear function of concentration between 4 and 40 μg/ml. (2) Maximum color develops immediately. (3) The color is stable for at least 16 hr. (4) There is greater reproducibility and reduction of interference by chloride ion and oxidants. It has been found possible to distinguish between heparin, heparin derivatives, and other polyuronides of connective tissue by comparing the effect of chlorides on the color yield in both procedures.