Fluorometric assay of sialic acid in the picomole range: A modification of the thiobarbituric acid assay

Fluorescence of the thiobarbituric acid reaction product of periodate-cleaved sialic acid is readily detected by excitation at 550 nm and analysis of emitted light at 570 nm. A fluorometric microassay is described which is 500-fold more sensitive than the usual spectrophotometric procedures and readily detects 10 ng (32 pmol) of sialic acid. Contamination by 2-deoxyribose from cellular material is easily detected by shifts of excitation maxima below 550 nm.