Synthesis of a polymeric imidazolium-embedded octadecyl ionic liquid-grafted silica sorbent for extraction of flavonoids

Abstract

In this work, a polymeric imidazolium-embedded octadecyl ionic liquid (poly(1-vinyl-3-octadecylimidazolium naphthalene sulfonate))-grafted silica (poly(C₁₈VIm⁺NapSO₃^-)@SiO₂) sorbent was prepared and applied as a solid-phase extraction (SPE) sorbent in extraction of flavonoids. The synthesized poly(C₁₈VIm⁺NapSO₃^-)@SiO₂ sorbent was characterized by X-ray photoelectron spectrogram (XPS) and fourier transform infrared spectroscopy (FT-IR). The thermodynamic and kinetic adsorption models of the prepared poly(C₁₈VIm⁺NapSO₃^-)@SiO₂ sorbent towards flavonoids were discussed by nonlinear fitting adsorption curve and the results indicated the thermodynamic adsorption model in this work was tended to be Freundlich model rather than Langmuir one and the pseudo-second order model could be used to describe the dynamic adsorption process. In addition, the adsorption amounts indicated the sorbent has satisfactory extraction capabities towards flavonoids. For investigating the influence of independent variables and their interactions on the extraction efficiency, a Box-Behnken design was used for optimizing three greatly influential parameters after performing single-factor experiments. The interaction energies between flavonoids and two ionic liquids were calculated to understand the adsorption mechanism. Under the optimal conditions, a method used for determining flavonoids was developed by combining SPE technique with high performance liquid chromatography (HPLC), and the developed method exhibited low limits of detection (0.25-0.4 μg L^-1), good linearities with correlation coefficients (R²) in the range of 0.9951-0.9996 and satisfactory recoveries ranging from 83.6% to 114.1%, which confirmed the proposed method could be successfully used to determine trace flavonoids in real samples.

Keywords: Flavonoids; Interaction energies; Polymeric ionic liquids; Response surface methodology; Solid-phase extraction; Thermodynamic and kinetic adsorption models.