A novel system of galangin–potassium permanganate–polyphosphoric acid for the determination of tryptophan and its chemiluminescence mechanism

A novel galangin–potassium permanganate (KMnO₄)–polyphosphoric acid (PPA) system was found to have an outstanding response to tryptophan (Trp). Trp determination using this KMnO₄–PPA system was enhanced significantly in the presence of galangin. A highly sensitive flow‐injection chemiluminescence (CL) method to determine Trp was developed based on the CL reaction of galangin–KMnO₄–Trp in PPA media. The presence of galangin, a member of the flavonol class of flavonoid complexes, greatly increased the luminous intensity of Trp in KMnO₄–PPA systems. Under optimized conditions, Trp was determined in the 0.05–10 µg/mL range, with a detection limit (3σ) of 5.0 × 10^?3 µg/mL. The relative standard deviation (RSD) was 1.0% for 11 replicate determinations of 1.0 µg/mL Trp. Two synthetic samples were determined selectively with recoveries of 98.4–100.1% in the presence of other amino acids. The possible mechanism is summarized as follows: excited states of Mn(II)^* and Mn(III ^* types are the main means of generating chemical luminescent species, and Trp concentration and luminescence intensity have a linear relationship, which enables quantitative analysis. Copyright © 2014 John Wiley & Sons, Ltd.