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Determination of Carboxymethylcellulose with Chromotropic Acid

University of Puerto Rico, Chemistry Department, Mayaguez 00708

ABSTRACT

Chromotropic acid (1,8-dihydroxynaph-thanene-3,6-disulfonie acid) in concentrated sulfuric acid was used to determine carboxymethylcellulose (CMC) isolated from milk, chocolate milk, chocolate and vanilla ice cream, and other products. For maximum color development, the reagent must be dissolved in concentrated H₂S0₄ and the CMC—reagent mixture must be heated for 60 to 90 min at 99 ± 1 C. The characteristic purple color developed has maximum absorbance at 570 nm. Color density increased as the degree of substitution of the CMC increased. Of 30 different food gums and related substances tested, only pectin and pectic acid gave the characteristic purple color. The reagent is more specific but less sensitive than the 2,7-naphthalenediol reagent. Interference from chocolate ingredients is less than when the 2,7-naphthalenediol and anthrone reagents are used and much less than with the phenol-H₂S0₄ reagent. In addition, determination is more rapid than with 2,7-naphthalenediol. Recoveries from various products were 88% and upwards, based on the addition of CMC added to water and carried through the entire and identical isolation procedure. The method will detect CMC in food products at 0.025% (w/w).

¹ Address until June 30, 1972: Department of Dairy & Food Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.