Electrochemical determination of synephrine by using nafion/UiO-66/graphene-modified screen-printed carbon electrode

The screen-printed carbon electrode (SPCE) was one step modified with graphene (GN) and UiO-66 composites in nafion solution as a portable sensor (nafion/UiO-66/GN/SPCE) for the detection of synephrine. The used GN and UiO-66 were well-characterized, exhibiting typical structures by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The nafion/UiO-66/GN/SPCE showed the maximum electrochemical signals for synephrine when comparing fabricated components in the cyclic voltammetric method. It was systematically investigated in modifier composition, modification volumes, pH, scan rate, and quantitative analysis ability. Under optimal conditions, the sensor exhibited a good detection limit (0.04 μmol L^-1) for synephrine with a linear range of 0.5 μmol L^-1 to 60 μmol L^-1 (r² = 0.995). The nafion/UiO-66/GN/SPCE had adequate reproducibility and stability with relative standard deviations lower than 2.01%. It was also applied to determine synephrine in the extract of Citrus aurantium L. with recoveries between 99.0% and 102.0%. The content of synephrine was in good agreement with that of the HPLC method. Based on its convenience and stability, the proposed nafion/UiO-66/GN/SPCE could be further developed as a portable and rapid detection sensor for natural active compounds in food, agricultural, and pharmaceutical fields.