Determination Of Sudan Dyes In Foodstuffs Using Reduced Graphene Oxide @Fe₃O₄ Magnetic Solid-phase Extraction

Objectives Sudan dyes are a class of lipophilic synthetic dyes. Because of their low cost and bright color, Sudan dyes are also attractive as food colorants to enhance the appearance of chili-containing and tomato sauce. However, these azo dyes are classified as category 3 carcinogens by the International Agency for Research Cancer（IARC）. In this work, a simple, effective and robust magnetic solid-phase extraction method was developed using magnetite/reduced graphene oxide nanoparticles（RGO@Fe₃O₄） as adsorbent coupled with high performance liquid chromatography for the simultaneous determination of Sudan dyes（Sudan I, II, III and IV） in foodstuffs.Methods The synthetic RGO@Fe₃O₄ was characterized by scan electron microscopy,transmission electron microscope, fourier transform infrared spectrometer, X-ray diffraction and vibrating sample magnetometer. Using magnetite/reduced graphene oxide nanoparticles（RGO@Fe₃O₄） as adsorbent magnetic solid phase extraction Sudan dyes in foodstuffs.The extraction parameters including the amount of RGO@Fe₃O₄（2.0 mg, 3.0 mg, 4.0mg, 5.0 mg）, extraction time（3 min, 6 min, 7min, 8 min）, efficiency elution solution（acetonitrile, acetone, chloroform, toluene）, elution time（5 min, 10 min, 15 min, 20 min）and elution volume（1 m L, 2 m L, 3 m L, 4 m L） were investigated in detail. Under optimum conditions, the proposed method was evaluated in terms of linearity, precision,repeatability, limits of detection（LODs）, limits of quantification（LOQs）, and recovery.The feasibility was further performed by a comparison with commercial alumina-N SPE cartridge.Results The XRD results suggest the presence of Fe₃O₄ on RGO. As shown in SEM,RGO displayed a thin paper-like morphology with some wrinkles, and Fe₃O₄ nanoparticles were anchored onto the RGO sheet. The room-temperature magnetization hysteresis curve was measured and the maximum saturation magnetization was 50.17 electromagnetic units（emu/g）. Under the optimized conditions, five milligrams of RGO@Fe₃O₄ were used, and the mixture was shaken for 7 min to adsorb the analytes. The pre-concentrated target analytes were desorbed from the isolated RGO@Fe₃O₄ with 3 m L of toluene by vigorously vortexing for 15 min.Such RGO@Fe₃O₄ based MSPE in combination with high performance liquid chromatography-variable wavelength detector gave the detection limits of 2.5 to 6.0μg/kg for Sudan I-IV in chili sauce, tomato sauce, chili powder and chili flake samples.The linearity of the method was in the range from 0.04 to 50 mg/m L with the correlation coefficients（r） ranging from 0.9998 to 0.9999 and the concentration factors for the analytes ranged between 66 and 76. The recoveries were 79.6%-108% at three spiked levels with the intra- and inter-day relative standard deviations of 1.2%-8.6% and 4.5%-9.6%. Furthermore, similar results were achieved using RGO@Fe₃O₄ and commercial Alumina N SPE cartridge.Conclusions In conclusion, a new RGO@Fe₃O₄-based MSPE combined with HPLC method was developed as an effective and useful protocol for pre-concentration and detection of banned Sudan dyes in different complicated food matrices. The proposed method is simple and low-cost. It facilitates accurate and reproducible determination of Sudan dyes in foodstuffs.