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Ortho-Tolidine and Sodium Hypochlorite for the Determination of Carrageenan and Other Ester Sulfates

Department of Chemistry, University of Puerto Rico, Mayaguez 00708

ABSTRACT

Carrageenan and other sulfated polysaccharides react with o-tolidine and sodium hypochlorite in a buffered medium to produce a purple or purplish-green color with maximum absorption at 545 to 550 nm, pH 1.4; 550 ran, pH 2.0; 565 to 570 nm, pH 2.5; and 590 to 595 nm, pH 3.0. Proteins, carboxylic, phos-phorylated and neutral polysaccharides do not react between pH 1.4 to 3.0. Color density varies with the degree of sulfation of the polysaccharides. Recoveries of up to 86% were obtained for carrageenan added to milk and to other dairy products. The standard deviation ranged from ± .49 to ± .51 mg of carrageenan when 10 mg of the hydrocolloid were added. The method will detect .025% of carrageenan.