Chemiluminescence of tryptophan enhanced by electrochemical energy

Electrochemiluminescence (ECL) was used to detect tryptophan in aqueous solutions in the presence of a brominating agent. Using platinum and glassy carbon electrodes, the ECL mechanism of tryptophan was studied. Tryptophan was oxidized at 0.78 V vs. sce in 0.1 M NaOH aqueous solution to the excited intermediate at a platinum electrode (0.44 V at a glassy carbon electrode). The intermediate was further oxidized and emitted light. The ECL signal was clearly observed when the applied potential was enough to oxidize the tryptophan. The ECL spectrum was measured, showing maximum emission peaks at 544 nm, 434 nm and 404 nm. Above 1.0 V, the brominating agent was oxidized which results in suppression of the ECL signal. A weak ECL signal was observed at an applied potential below 0.5 V, which indicates that this reaction is chemiluminescence (CL), enhanced by the applied potential. This method cannot be used for routine analysis because of the high detection limit of tryptophan (1.0 μmol), but can be used to obtain emission mechanism information.