Rapid, Sensitive, and Selective Assay for Tryptophan in Serum

Abstract We have developed a rapid, selective, and sensitive fluorometric procedure for measuring tryptophan in serum. This assay is based on the facile reaction of tryptophan with aqueous formaldehyde; the concentration of the amino acid is measured from the diminution in its fluorescence as the reaction proceeds. Compared to other assay procedures, this procedure has the advantage of being sensitive to the amino acid, but unresponsive to other indole derivatives such as tryptamine and 5-hydroxytryptamine. Concentrations of tryptophan as low as 0.5 mg/liter may be assayed in 15 min.