No abstract

A simple ultrasound-assisted dispersive micro-solid phase extraction method based on graphene-oxide (GO) nanosorbents (UAD-m-SPE), followed by high performance liquid chromatography-ultraviolet detection (HPLC-UV) was developed for the simultaneous determination of theophylline, theobromine and caffeine in different infusion tea samples. GO was synthesized by Hummers method and characterized with field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. The GO sorbent was dispersed in the sample solution with the assistance of ultrasound to enhance adsorption and desorption performance and rates. The main parameters influencing the extraction efficiency, including desorption solvent (type and volume), sorbent dosage, adsorption time, desorption time, and ionic strength were studied and optimized by a one factor at a time method. The best performance of the method was achieved with 3 mg mL À1 of GO, adsorption time of 15 min, desorption time of 4 min, salt concentration of 5%, and 100 mL of desorption solvent (alkaline methanol). Under the optimized conditions, the limit of detection (LOD) and limit of quantification (LOQ) were attained in the ranges 0.11-0.90 ng mL À1 and 0.37-3.00 ng mL À1 , respectively. The method showed a good linearity in the range of 0.003-5 mg mL À1 with a coefficient of determination (R 2 ) higher than 0.986. The repeatability and reproducibility of the method were 1.80% and 2.9%, respectively. The developed technique (GO-UAD-m-SPE) was successfully applied to the determination of the analytes in beverage tea samples including black, white, oolong, and green teas with the relative recoveries in the range of 84.6-113.6%.