Determination of Uronic Acids in Cellulosic Materials

Abstract

Naturally-occurring cellulosic fibres appear to be a more or less intimate association of cellulose with other constituents, generally referred to as incrusting substances. A portion of these extraneous materials appears to be com posed of uronic acids, presumably contained in the pectic substance of the fibres. Many of the important properties of these fibres, such as tensile strength, moisture and dye absorption, and viscosity in cuprammonium solution have frequently been considered as related to the presence of small quantities of pectin. In order to study this relation ship in greater detail, it was necessary to develop a method for the quantitative estimation of pectin or its constituent uronic acids. Available methods, based on the evolution of carbon dioxide during treatment of the uronic acid with a boiling solution of hydrochloric acid, were found to fail when cellulose or other carbohydrate materials were present, since these substances also decompose with the evolution of some carbon dioxide. An investigation of the rates of evolution of carbon dioxide showed that pure uronic acids evolved carbon dioxide at a rapid rate and that the evolution of gas was complete in several hours. On the other hand, carbohydrates, free of uronic acids, evolved carbon dioxide at a much slower but approximately con stant rate during the entire treatment. It was found that this difference in rates could be utilized for the estimation of uronic acids, even when they are mixed with large pro portions of cellulosic materials. A detailed description of the apparatus and its manipulation is given.