Comparison of reduction methods for gas chromatography/mass spectrometry identification and quantitation of uronic acids in acidic polysaccharides

Abstract

Four different reduction procedures were evaluated for their efficiency in dideuterating uronic acids in acidic polysaccharides. A method using 8 M urea to dissolve the polymers and 1-chyclohexyl-3-(2-morpholinoethyl)-carbodiimide metho-p-toluene sulfonate (CMC) to form uronide esters provided the best uronide dideuteration and uronic acid and neutral hexose sugar recoveries. Of the total uronic acid detected by a colorimetric assay, 20–30% was recovered as specific uronic acids from low-viscosity biopolymers by gas chromatography—mass spectrometry when this reduction procedure was employed. Lower and more variable recoveries of uronic acids were obtained from high-viscosity polysaccharides. The technique provided positive identification of the uronic acids in all five acidic polymers tested, even when the polymer also contained the corresponding neutral sugar analogue. Although quantitative recovery of uronic acids was not obtained, the technique nevertheless provides useful information on the relative contribution of uronic acids and neutral sugars in unpurified low-viscosity polymer preparations.