Highly sensitive determination of capsaicin with tris(2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence

A highly sensitive tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)₃²⁺] electrogenerated chemiluminescence (ECL) detection method for the determination of capsaicin has been developed. In this study, capsaicin was worked as a coreactant in the oxidative-reduction pathway of the Ru(bpy)₃²⁺ ECL. The oxidation of Ru(bpy)₃²⁺ together with coreactant capsaicin on a bare glassy carbon electrode at an applied potential of + 1.10 V vs. Ag/AgCl (3 M NaCl) led to a strong ECL emission. The Ru(bpy)₃²⁺ ECL emission of capsaicin was strongly dependent upon the buffer solution pH, in which a strong ECL was obtained in alkaline buffer solution. Under the optimized conditions, the present Ru(bpy)₃²⁺ ECL detection method showed a linear response to capsaicin in the linear range from 1.0 × 10^-7 M to 1.0 × 10^-4 M with a limit of detection of 9.4 × 10^-8 M (S/N = 3). In addition, the present method can detect dihydrocapsaicin and nordihydrocapsaicin with a detection limit of 1.9 × 10^-7 M and 2.2 × 10^-7 M, respectively. The present ECL method shows good analytical performance for capsaicinoids in terms of linear dynamic range and detection limit compared to those obtained at other electrochemical methods even without the employment of additional modification of electrode surfaces to enhance the detection responses. In addition, no analyte preconcentration was required. The recovery tests performed for spiked capsaicin in real pepper samples were satisfactory with the recovery from 95% to 103%. To the best of our knowledge, this is the first report on the application of ECL for the quantitative determination of capsaicinoids. Since the present method is very simple, fast and sensitive, it could be applied for the determination of capsaicin in food and pharmaceuticals.