Selective determination of caffeine in foods with 3D-graphene based ultrasound-assisted magnetic solid phase extraction.

An efficient method was applied for extraction of caffeine in food samples. Three-dimensional graphene-Fe3O4 (3D-G-Fe3O4) nanoparticles was successfully synthesized and used as adsorbent in magnetic solid phase extraction (MSPE) step. The properties of synthesized adsorbent were characterized by fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods. The influence of main parameters of extraction procedure such as ultrasound parameter, amount of nanoparticles, pH, salt concentration and desorption condition were investigated and optimized. Under the optimized experimental conditions, the figure of merit results showed excellent linear dynamic range (LDR) of 0.5-500 µg mL-1, with determination coefficient (R2) higher than 0.996 and limit of detection (LOD) of 0.1 µg mL-1. Intra- and inter-day relative standard deviations (RSDs) were less than 5.9 and 7.1%, respectively. The method was successfully applied for determination of caffeine in different food samples.