A novel electrochemical assay for aspartame determination via nucleophilic reactions with caffeic acid ortho-quinone

Cyclic voltammetry (CV) in a pH 7.0 phosphate buffer solution containing aspartame (ASP) and caffeic acid (CAF) was studied. In sharp contrast to untreated electrodes, two distinct redox peaks were observed at preanodized screen-printed carbon electrodes (SPCE*) due to the formation of a homopolymer poly( CAF) and a copolymer poly(CAF-ASP). The characteristics of the polymer film-modified electrodes were well-characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), photoelectron spectroscopy (XPS) and the water contact angle technique. Electrochemically induced polymerization mechanisms were discussed. Current responses from poly(CAF-ASP) were employed for ASP determination, and a linear dynamic range from 0.05 mu M to 10 mu M was obtained using differential pulse voltammetry (DPV). The limit of detection (LOD, S/N = 3) was 0.0076 mu M, the limit of quantification (LOQ, S/N = 10) was 0.0256 mu M, and sensitivity was 12.067 mA mu M-1. The relative standard deviation (RSD) was less than 5%, indicating good precision. Common additives in soft drinks do not interfere with the ASP analysis. The proposed assay was applied for the determination of ASP in two soft drinks using the standard addition method, and recoveries in the range of 103.0-106.7% and 97.3-106.4% were obtained for Coca-Cola and Coke Zero, respectively. A reference high-performance liquid chromatography (HPLC) was applied to validate the proposed method, and good agreement was obtained. (C) 2019 Elsevier Ltd. All rights reserved.