Determination of synthetic pigments in beverages by ionic liquid based magnetic solid phase extraction-high performance liquid chromatography

The strict limit standards for synthetic pigments maximum usage were set in our country. To ensure food safety, effective extraction and determination of synthetic pigments in food are necessary. In this study, a poly(ionic liquid)-modified magnetic nanoparticles was synthesized and served as an adsorbent of magnetic solid-phase extraction (MSPE). The structure, morphology, and magnetic property of the adsorbent were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometer. The extraction performance of the adsorbent was studied for four synthetic pigments including tartrazine, sunset yellow, temptation red, and brilliant blue. According to the adsorption efficiency of typical anionic and cationic dye, the effective extraction of the adsorbent for four synthetic pigments was attributed to the strong electrostatic attraction as well as the π-π and hydrophobic interactions between the adsorbent and the analytes. The main parameters influencing the extraction efficiency, such as adsorbent amount, adsorption and desorption time, and salt addition, were optimized. Under the optimized extraction conditions, the performance and applicability of the proposed method were investigated by combining with MSPE and high-performance liquid chromatography. The four synthetic pigments had a satisfactory linearity with correlation coefficients ranged from 0.992 2 to 0.997 5. The limits of detection (S/N=3) and limits of quantitation (S/N=10) were 1-3 μg/L and 2.5-10 μg/L, respectively. The method could be successfully used for the determination of synthetic pigments in two beverages (Jianlibao and Boluopi). The relative recoveries at three different spiked levels (25, 100, and 250 μg/L for sunset yellow, temptation red and brilliant blue, 50, 200, and 500 μg/L for tartrazine) ranged from 71.4% to 113.0%, and the relative standard deviations were less than 10.9% (n=3). This work provides a promising sample preparation technique for the analysis of synthetic pigments in food.