Electrochemiluminescence of Luminol in Alkaline Solution at a Paraffin-Impregnated Graphite Electrode

Abstract

The behavior of luminol electrochemiluminescence (ECL) at a paraffin-impregnated graphite electrode (PIGE) at different applied potentials was studied. Five ECL peaks were observed at 0.31, 0.59, 1.09, 1.54, and -0.58 V versus SCE, respectively, being related to potential scan direction and ranges, N2, O2, pH of the solution, and KCl concentration. The emission spectra of various ECL peaks at different potentials showed that all ECL peaks were initiated by luminol reactions. X-ray diffraction demonstrated that a simple mixture was formed between graphite and paraffin. The fluorescence spectra on the surface of the PIGE suggested that certain groups on the graphite were oxidized when the positive potential was applied to the electrode. In the presence of O2, three main ECL peaks were obtained in 0.1 mol/L KCl at pH 12.2. The ECL peak at 0.59 V with a shoulder is likely due to the reaction of luminol radicals with O2 and further electrooxidation of luminol radicals. The ECL peak at 1.54 V was suggested to be due to the electrooxidation of OH- to HO2- at higher potential and then to O2-, which reacted with luminol to produce light emission. Moreover, the oxygen-containing functional groups formed by the oxidation of the surface of the graphite electrode might enhance the ECL. At -0.58 V, the dissolved oxygen in solution was reduced to HO2-, resulting in light emission. At a potential higher than 1.64 V, ClO- was formed, leading to a broad emission wave and enhancement of the ECL peak at -0.58 V upon the reversal scan. Under nitrogen atmosphere, an ECL peak appeared at 1.09 V. At this potential, OH- was oxidized to O2, followed by the reaction with luminol to generate light emission. At pH 13.2 or 0.5 mol/L KCl, the shoulder of the ECL peak at 0.59 V became an ECL peak at 0.31 V. The conversion of luminol radicals into excited 3-aminophthalate may undergo two routes. Under these conditions, two routes might proceed at a different rate to form another ECL peak. It is concluded that luminol ECL could be readily excited by various oxygen-containing species electrogenerated at different applied potentials. Three strong ECL peaks obtained at different potentials on the PIGE might be of a potential to improve analytical selectivity and sensitivity for the detection of some analytes.

A Review of Electrogenerated Chemiluminescent Biosensors for Assays in Biological Matrices

“…The mechanism for luminol ECL has been studied by various groups and depends on the oxidant species and voltage applied [44][45][46][47][48][49]. The reaction occurs most efficiently under alkaline (pH 8.0-8.5) conditions, when luminol has been deprotonated (pK a1 = 6.2).…”

A Demonstration of Simultaneous Electrochemiluminescence

“…12 The overall reaction (eq 12) involves light production in both sides of the cell. Thus, simultaneous anodic and cathodic ECL phenomena are achieved and are visible to the naked eye.…”

Cathodic electrochemiluminescence of acetonitrile, acetonitrile–1,10‐phenanthroline and acetonitrile–ternary Eu(III) complexes at a gold electrode

“…The H-type ECL cell was constructed as described previously (19). A 7.0 × 9.0 mm 2 gold foil served as the working electrode, a platinum wire as the counter-electrode and an Ag/AgCl wire as the reference electrode.…”