Carboxymethylcellulose (CMC) was hydrolyzed in aqueous sulfuric acid at -90 OC to yield substituted glucoses which were analyzed by proton nuclear magnetic resonance. A procedure for the measurement of the degree of substitution (DS) of CMC was developed. Agreement of the DS determlned in thls procedure with that obtalned from a standard ASTM method is generally good. Additionally, the average distribution of the carboxymethyl substituents in CMC was also measured from the same spectrum. This result showed that the reactivity of the hydroxyls in cellulose toward carboxymethylation varied in the order OH(2) > OH(6) > OH(3), where the numbers In parentheses represent the carbon posllions in the anhydroglucose unit.Carboxymethylcellulose (CMC) is an important industrial polymer which finds wide application in detergents, textiles, paper, food, drugs, and oil well drilling operations, among others. In 1974, over 75 million pounds were produced in the United States alone ( I ) . Many of the properties of CMC in actual applications depend to a large extent on two key structural parameters, namely, the degree of substitution (DS) of the hydroxyl groups on the anhydroglucose unit and the distribution of the carboxymethyl substituents.A spectrophotometer is described in which a linear photoarray using charge-coupled technology is used as a detector. The device can access 260 nm of the visible spectrum in as little as 8 ms. Using the detector's integrating character, the exposure time is programmed by computer so that the signalto-noise ratio can be substantially Improved. A model for the variance as a function of wavelength and absorbance was developed and validated.