Magnetic metal-organic frameworks for fast and efficient solid-phase extraction of six Sudan dyes in tomato sauce. 
Magnetic solid-phase extraction is an effective and useful technique to preconcentrate trace analytes from food samples.  In this study, a magnetic trimeric chromium octahedral metal-organic framework (Fe3O4-NH2@MIL-101) was fabricated and characterized.  Fe3O4-NH2@MIL-101 was applied as an adsorbent of magnetic solid-phase extraction combined with high performance liquid chromatography to effectively isolate and simultaneously determine six Sudan dyes (Para Red, Sudan I-IV, and Sudan Red 7B) from tomato sauce.  Potential factors affecting the MSPE were investigated in detail, and adsorption efficiency of Fe3O4-NH2@MIL-101 was compared with those of conventional adsorbents, such as neutral alumina, HLB, and C18.  The developed method facilitated the extraction with using only 3 mg of adsorbent in 2 min.  In addition, enhancement factors of 50, linear range of 0.01-25 μg/mL, and detection limit (S/N = 3) of 0.5-2.5 μg/kg were obtained.  The intra-day and inter-day recoveries for spiked Sudan dyes were in the range of 72.6%-92.9% and 69.6%-91.6%, respectively, with relative standard deviations of ≤9.2%.