Sensitive Electrochemical Sensor Based On an Aminated\nMIL-101(Cr) MOF for the Detection of Tartrazine

Abstract

The aminated metal–organic\nframework H₂N-MIL-101­(Cr)\nwas used as the carbon paste electrode (CPE) modifier for the determination\nof tartrazine (Tz) in soft drinks. The amino material was characterized\nby electrochemical impedance spectroscopy and showed significantly\nfaster electron transfer with lower charge-transfer resistance (0.13\nkΩ) compared to the electrode modified with the unfunctionalized\nMIL-101­(Cr) material (1.1 kΩ). The H₂N-MIL-101­(Cr)-modified\nCPE [H₂N-MIL-101­(Cr)-CPE] was then characterized by cyclic\nvoltammetry (CV) using [Fe­(CN)₆]^3– and\n[Ru­(NH₃)₆]³⁺ ions as the redox probes,\nshowing good accumulation of [Fe­(CN)₆]^3– ions on the electrode surface. A CV scan of Tz in Britton Robinson\nbuffer solution revealed an irreversible system with an oxidation\npeak at +0.998 V versus Ag/AgCl/KCl. Using CV and differential pulse\nvoltammetry, an electrochemical method for quantifying Tz in aqueous\nmedium was then developed. Several parameters that affect the accumulation\nand detection steps were optimized. Optimal detection of Tz was achieved\nafter 180 s of accumulation in Britton Robinson buffer solution (pH\n2) using 2 mg of H₂N-MIL-101­(Cr) material. Under optimal\nconditions, the sensor exhibited a linear response in the concentration\nrange of 0.004–0.1 μM and good detection sensitivity\n(35.4 μA μM^–1), and the detection limit\nfor Tz was found to be 1.77 nM (S/N = 3). Satisfactory repeatability,\nstability, and anti-interference performance were also achieved on\nH₂N-MIL-101­(Cr)-CPE. The sensor was applied to commercial\njuices, and the results obtained were approximately similar to those\ngiven by UV–vis spectrophotometry.