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Anamperometric sensor based on an inkjet-printed graphene electrode (IPGE) modified with amine-functionalized montmorillonite (Mt-NH2) for the electroanalysis and quantification of gentisic acid (GA) has beendeveloped. The organoclay used as IPGE modifier was prepared and characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, CHN elemental analysis, and thermogravimetry. The electrochemical features of the Mt-NH2/IPGE sensor were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibited charge selectivity ability which was exploited for the electrochemical oxidation of GA. The GA amperometric response was high inacidic medium (Brinton-Robinson buffer, pH 2) due to favorable interactions between the protonated amine groups and the negatively charged GA. Kinetic studies were also performed by cyclic voltammetry, and the obtained electron transfer rate constant of 11.3s-1 indicated a fast direct electron transfer rate of GA to the electrode. An approach using differential pulse voltammetry was then developed for the determination of GA (at + 0.233V vs. a pseudo Ag/Ag+ reference electrode), and under optimized conditions, the sensor showed high sensitivity, a wide working linear range from 1 to 21μM (R2 = 0.999), and a low detection limit of 0.33μM (0.051 ± 0.01mgL-1). The proposed sensor was applied to quantify GA in a commercial red wine sample. The simple and rapid method developedusing a cheap clay material could be employed for the determination of various phenolic acids.

This work describes a new sensitive sensor for the simultaneous electrochemical determination by square wave anodic stripping voltammetry of Cd2+ and Pb2+ ions in aqueous solution, based on a disposable ink-jet-printed graphene electrode (IPGE) modified by a thin film of montmorillonite (Mont) clay mineral. The clay was characterized by X-ray diffraction and scanning electron microscopy while the Mont–IPGE was analyzed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry before its exploitation for sensing studies. EIS results revealed a low electron transfer rate on Mont–IPGE during the electro-oxidation of [Fe(CN)6]3−. The stripping response on both Cd2+ and Pb2+ analytes was improved by the in situ co-deposition with bismuth, added to the electrolyte solution, on the clay substrate. The proposed electrode showed great stability and good reproducibility. The key experimental parameters governing the stripping analysis of Cd2+ and Pb2+ were optimized. A linear relationship between peak currents and concentrations of the analytes was obtained in the range from 0.01 to 0.21 µM, leading to detection limits of 0.42 nM for Cd2+and 1.14 nM for Pb2+ ions, respectively (S/N = 3). The sensitivities to Cd2+ and Pb2+ ions were 921.8 A cm−2 M−1 and 1960.8 A cm−2 M−1, respectively. The Mont–IPGE sensor was used for the quantification of lead and cadmium in a mineral water.