MIL-101 (Cr): Synthesis and simultaneous electrochemical determination of uric acid and theophylline using MIL-101 (Cr) modified electrode

This paper presents the synthesis of metal-organic frameworks in the MIL (Materials Institute Lavoisier) series using a hydrothermal process. Our research revealed that MIL-101 was formed at the early synthetic stage, approximately eight hours, followed by the formation of MIL-88B with further prolongation of the hydrothermal time. The morphology of the octahedral shape for MIL-101 transformed into the rode-like shape of MIL-88B, accompanied by a decrease in the surface area. The electrode modified by MIL-101 exhibited electrochemical activity towards uric acid and theophylline better than that modified by MIL-88B. We also developed a glassy carbon electrode (GCE) modified by MIL-101 for simultaneous uric acid and theophylline detection. Electrochemical sensing features were investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The calibration curves for uric acid and theophylline were obtained in the 0.20–1.69 µM range. The detection limits (3σ) were 0.12 µM and 0.13 µM for uric acid and theophylline, respectively. Notably, using a standard addition method, the present approach was used to determine URI and THE in urine samples, achieving exceptional recoveries. The proposed electrochemical sensor also revealed good reproducibility, repeatability, and long-term stability.