Abstract
Tyrosine (l-Tyr), which is found in basic foods, is a nonessential amino acid and a metabolite of phenylalanine, has many roles in human metabolism, and is important in maintaining nutritional balance. In this study, an electrochemical method has been presented to determine low levels of l-Tyr using an electrochemically treated pencil graphite electrode (EPGE) via overoxidation of graphite surface and intercalation of Li+ ions into graphite by cyclic voltammetry in the potential range between −0.3 and 2.0 V. Characterization studies of the EPGEs were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, and cyclic voltammetry. The determination of l-Tyr was performed by differential pulse voltammetry, and the investigation of electrochemical properties of l-Tyr was conducted by cyclic voltammetry. The results showed that the EPGE presents high electrocatalytic performance and has a low detection limit (0.12 μM) for determining l-Tyr with a wide linear range from 1.0 to 500 μM. The selectivity of prepared EPGE was investigated in the presence of organic species. The determination of l-Try was performed in yoghurt and milk samples and good results were obtained with recoveries between 95.7% and 103.1%. Stability and repeatability studies further demonstrate the applicability of the sensor.