A method for the simultaneous estimation of free and ketosidically bound sialic acids.

Various methods for the estimation of free and ketosidically bound sialic acid were investigated for accuracy and specificity. It was found that oxidation with 0.025 M sodium metaperiodate in pH 7.0 phosphate buffer at room temperature for 20 min provided a simple, rapid, sensitive method whereby both the free and the ketosidically bound acid present in a mixture could be quantitatively analyzed. On completion of the oxidation step, the bound sialic acid is estimated with resorcinol reagent and the free sialic acid with thiobarbituric acid reagent. Oxidation under these conditions permitted a facile analysis of mixtures of bovine submaxillary mucin and free N-acetylneuraminic acid, whereas the Warren thiobarbituric acid procedure gave an erroneous value for free sialic acid.