Voltammetric determination of quinine and its n-oxide using silver solid amalgam electrodes

For the first time, a voltammetric method for the determination of quinine using silver solid amalgam electrodes has been developed. The highest currents and a clear quinine reduction peak were achieved by a mercury meniscus-modified silver solid amalgam electrode ( m -AgSAE). Quinine is reduced on m -AgSAE as a single irreversible peak in both slightly acidic and alkaline media. An optimal pH of 8 was selected and maintained using the Britton-Robinson buffer. The quinine reduction peak was adsorptive, promoting analyte accumulation on the electrode surface. Under optimal conditions, a calibration curve for the voltammetric determination of quinine was obtained, with a linear range from 2.0 10⁻⁶ to 2.0 10⁻⁵ M and a limit of detection of 1.7 10⁻⁶ M. The developed method was tested on tonic beverages. The results were statistically processed and confirmed by high-performance liquid chromatography with a diode-array detector as a reference method. The relative error of determination did not exceed 5 %. The proposed method is fast, portable, and suitable for routine analysis. Keywords: voltammetry, alkaloids, quinine, N-oxide quinine, solid amalgam electrodes.