Two methods are described for locating the 0- (carboxymethyl) groups in O-(carboxymethyl)guar. In Method I, 0-(carboxymethyl)guar was depolymerized by methanolysis, the 0-(carboxymethyl) groups were reduced, and the mixture of methyl glycosides and 0-(2-hydroxyethyl)-substituted methyl glycosides was converted into a mixture of per-0-acetylated alditols and partially O-(2acetoxyethyl)ated, partially 0-acetylated alditols. Analysis of these alditols by gasliquid chromatography-mass spectrometry allowed the positions of substitution of the 0-(carboxymethyl) groups on the galactosyl groups and mannosyl residues to be determined. However, this method did not distinguish between O-(carboxymethyl) substitution on 4-linked and 4,6-linked mannosyl residues. This limitation was overcome by the more-detailed analysis provided by Method II, in which 0-(carboxymethyl)guar was carboxyl-reduced, the product methylated, the glycosyl residues hydrolyzed, the sugars reduced, and the alditols acetylated to yield a mixture of partially 0-acetylated, partially 0-methylated alditols and partially 0-acetylated, partially 0-(2-methoxyethyl)ated, partially 0-methylated alditols. These derivatives, when separated and quantitated by g.l.c., and identified by g.l.c.-m.s., gave a quantitative measure of every type of carboxymethyl substitution in guar. INTRODUCI'ION Guar, a galactomannan isolated from the seed of guar (Cyamopis tetrugonoloh), has a backbone of j3-(1+4)-linked D-rIWinOSy1 residues, of which -60 percent are substituted at O-6 with a single a-D-g&CtOSyl group. Guar that is treated with chloroacetic acid yields 0-(carboxymethyl)-substituted guar. Method&* that can determine the points of substitution in O-(carboxymethyl)cellulose are not applicable to 0-(carboxymethyl)guar. We now present two methods for identifying and quantifying the positions of substitution of the carboxymethyl