Flow-injection chemiluminescence determination of tryptophan through its peroxidation and epoxidation by peroxynitrous acid

A flow-injection chemiluminescence method for the determination of tryptophan was proposed, which was based on an intense chemiluminescence of tryptophan in hydrogen peroxide-nitrite-sulfuric acid medium. The chemiluminescence reaction was attributed to peroxidation and epoxidation of tryptophan by peroxynitrous acid, and subsequent decomposition of the formed dioxetane. The chemiluminescence intensity was linear with tryptophan in the range of 6.0 × 10−7 to 3.0 × 10−5 mol l−1 and the limit of detection (S/N = 3) was 1.8 × 10−7 mol l−1. The proposed method was applied to the analysis of tryptophan in pharmaceutical preparations and human serum.