A carbon paste electrode (CPE) modified with a metal-organic framework composite of type MIL-101(Fe) is described for determination of citric acid (CA). The electrochemical activity of the modified CPE was studied by cyclic voltammetry and differential pulse voltammetry. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, N2 adsorption-desorption isotherms and X-ray powder diffraction were used for characterization of the MIL-101(Fe). Under optimized electrochemical conditions, the anodic peak current, best measured at working potentials around 0.02 V (vs. Ag/AgCl); decreases linearly in the 5.0 to 100 μM CA concentration range, and the detection limit is 4.0 μM (at S/N = 3). The electrode exhibits good selectivity for CA, with no significant interference in the wide pH range of 3.0 to 9.0. The electrochemical sensitivity of the MIL-CPE is -0.67 μA·μM-1·cm-2. The method was successfully applied to the determination of CA in some commercial beverages. The good recoveries (98-102%) and the agreement of data with those obtained by HPLC indicate the applicability of the method. Graphical abstract Schematic presentation of a new modified carbon paste electrode based on the metal-organic framework of type MIL-101(Fe) for the simple and sensitive determination of citric acid. The results show the MIL-101(Fe)-modified electrode to have good selectivity for citric acid and to enable real sample analysis.
Keywords: Beverage; Cyclic voltammetry; Differential pulse voltammetry; Electrochemistry; MOFs; Porous materials; Sensor.