Preparation of polydopamine-coated magnetic nanoparticles for dispersive solid-phase extraction of water-soluble synthetic colorants in beverage samples with HPLC analysis

A facile and sensitive dispersive solid-phase extraction (D-SPE) method for the extraction and enrichment of four representative synthetic colorants prior to high performance liquid chromatography analysis was introduced. As highly efficient adsorbents, polydopamine-coated Fe 3 O 4 nanoparticles (Fe 3 O 4 @PDA NPs) were prepared by a simple and green procedure. Several factors affecting the extraction efficiency, mainly including the polymerization time of dopamine, pH of the sample solution, the amount of adsorbent, extraction time and the desorption conditions, were systematically studied. Under the optimized conditions, the enrichment factors for the four colorants were both higher than 176. The limits of detection (LODs) for the established d-SPE-HPLC method were found to be 0.20–0.25   μg   L −1 , which were lower than most chromatographic methods previously reported for synthetic colorant analysis. When used for quantitative analysis, wide linearity ranges (1–500   μg   L −1 for amaranth and Ponceau 4R, and 0.80–500   μg   L −1 for sunset yellow and allure red) were achieved with good correlation ( R 2 ≥0.9995). The developed method was also successfully applied to the analysis of colorants in beverage samples with satisfactory results, demonstrating its reliability and feasibility in real sample analysis.