Sensitive and selective voltammetric method for determination of quinoline alkaloid, quinine in soft drinks and urine by applying a boron-doped diamond electrode

Abstract

In this paper, for the first time, the method of determination of the alkaloid of quinoline derivation, quinine (QN), was developed. A miniatured planar electrochemical cell with a working electrode, a boron-doped diamond electrode (BDDE), was used. QN is easily oxidized in a strongly acidic environment – 2 M HClO4 at a potential of Epa = +1.42 V, and in an alkaline environment.Epa = +0.94 – +1.18 V, depending on the pH of the medium at the surface of BDDE. Also, QN is reduced within wide pH ranges at the background of the Britton–Robinson buffer (Epc = −1.11 – −1.51 V). This enables the simultaneous determination of QN by anodic and cathodic currents. The conditions for the determination of QN were optimized. Calibration curves under optimal conditions were obtained using differential pulse voltammetry (DPV) and square-wave voltammetry (SWV). The limit of detection of QN according to the cathodic peak is at the level of 10−7M. According to the peak of QN oxidation, the sensitivity is worse, and the limit of detection of QN is at the level of 10−6M. The developed method was tested in the analysis of soft drinks. The results were compared with those of high performance liquid chromatography. The obtained results were statistically processed using the relative errors and Student t-test. Uric acid, nicotine, and caffeine, which can often be present in biological fluids, do not affect the oxidation and reduction of QN on BDDE. Various methods of urine sample preparation for voltammetric analysis were investigated. The proposed method can determine QN in urine at the level of 1.0 μg/ml of urine.