Determination of Uronic Groups in Polysaccharides

Abstract

URONIC groupings occurring in polysaccharides are usually determined by measuring the evolution of carbon dioxide on heating with 12 per cent hydrochloric acid. Campbell, Hirst and Young¹ have pointed out that a small amount of carbon dioxide is liberated under these conditions from a number of pure sugars and polysaccharides in which the presence of uronic groups is not presumed, though not necessarily disproved. The evolution of carbon dioxide from certain acids that might be formed by the degradation of polyuronides was reported by Norman and Martin². In an investigation of plant celluloses carried out two to three years ago at the Rothamsted Experimental Station, it was sought to establish whether the carboxyl groups demonstrably present were of the uronic type. Yields of carbon dioxide of the order of 0.2–0.3 per cent were considered to be unreliable for the reason just given, and accordingly recourse was had to the determination of the rate of evolution of carbon dioxide from such substances under standard conditions in the hope that this might be employed for demonstrating the presence or absence of uronic groups. No absolute value is involved inasmuch as it is the rate of absorption that is measured, and this is in part a characteristic of the size of apparatus in relation to the sample, the air stream, and absorbing device employed. The oil bath temperature was maintained at 140°, and a constant rate of aeration secured. The distillation was not carried out in an atmosphere of nitrogen; nevertheless the total yields of carbon dioxide from pure substances were not higher than those given by Campbell, Hirst and Young¹.