Facile preparation of nano-g-C₃N₄/UiO-66-NH₂ composite as sorbent for high-efficient extraction and preconcentration of food colorants prior to HPLC analysis

In this work, the nano-g-C₃N₄/UiO-66-NH₂ composite was prepared by one-step solvothermal method. The as-prepared composite was characterized by scanning electron microscopy, Brunner-Emmet-Teller measurement, energy dispersive spectrometer, X-ray diffraction, and Fourier transform infrared spectroscopy. By using nano-g-C₃N₄/UiO-66-NH₂ composite as sorbent, a dispersive solid-phase extraction coupled with high-performance liquid chromatography was developed to sensitive analysis of food colorants including tartrazine, amaranth, carmine, sunset yellow, allura red and bright blue. The experiment parameters including the amount of sorbent, adsorption time, the pH of adsorption solution, desorption time, desorption solvent, the pH of desorption solution as well as the proportion between desorption solvent and buffer solvent were investigated. Under the optimized conditions, the limits of detection (S/N = 3) and limits of quantitation (S/N = 10) were determined in the ranges of 0.08–0.8 and 0.2–2.0 ng/mL, respectively. With the developed sample pretreatment method, carmine and brilliant blue were determined from blueberry juice by HPLC-DAD. The contents were calculated as 1.53 µg/mL and 0.17 µg/mL, respectively.