Simultaneous determination of direct yellow 50, tryptophan, carbendazim, and caffeine in environmental and biological fluid samples using graphite pencil electrode modified with palladium nanoparticles.

The present study reports the development of graphite pencil electrode modified with palladium nanoparticles (PdNPs) and its application as an electrochemical sensor for the simultaneous detection of direct yellow 50, tryptophan, carbendazim and caffeine in river water and synthetic urine samples. The combination involving the conductive surface of the graphite pencil electrode (GPE) and the enlargement of the surface area caused by the use of palladium nanoparticles (PdNPs) led to the improvement of the analytical performance of the proposed device. The surface of the GPE-PdNPs was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The charge transfer kinetics of the electrode was evaluated based on the electrochemical analysis of the potassium ferricyanide redox probe. Using square wave voltammetry (SWV), well-defined and fully resolved anodic peaks were detected for the analytes, with peak-to-peak potential separation not less than 200 mV. Under optimised conditions, the following linear range concentrations were obtained: 0.99-9.9 μmol L for direct yellow 50; 1.2-12 μmol L for tryptophan; 0.20-1.6 μmol L for carbendazim; and 25-190 μmol L for caffeine. The sensor showed good sensitivity, repeatability, and stability. The device was successfully applied for the determination of analytes in urine and river water samples, where recovery rates close to 100% were obtained. Due to its low cost and reusability by simple polishing, the sensor has strong potential to be used as an electrochemical sensor for the determination of different analytes.