Spectrophotometric determination of total uronic acids in seawater using cation-exchange separation and pre-concentration by lyophilization

A technique is described for the measurement of total uronic acids in coastal seawater using a spectrophotometric method after separation and pre-concentration. Uronic acids in seawater are separated through cation-exchange and pre-concentrated by freeze drying. The concentrations of total uronic acids are determined based on a sulfamate/m-hydroxydiphenyl assay in concentrated sulfuric acid. This modified approach has been tested in estuarine and coastal water of Galveston Bay where the concentrations of total uronic acids ranged from 3.2 to 6.5µM-C. Uronic acids accounted for 7.9-12.3% of the total carbohydrate content. These results suggest that uronic acids are one of the important compound classes of carbohydrates in seawater. The detection limit was 0.08µM for uronic acids or 0.5µM-C, and the precision was <=10% for values close to the detection limit.