Selective adsorption and separation of illegal cationic dyes from foodstuffs with anionic polyelectrolyte functionalised metal-organic frameworks

A novel adsorbent, poly(sodium 4–styrenesulfonate) modified MIL-101(Cr)–NH₂, was successfully prepared. Owing to its high surface area and degree of negative surface charge, it enables effective adsorption and separation of illegal cationic dyes, such as rhodamine B, pararosaniline, and auramine O, from foodstuffs prior to high performance liquid chromatography analysis. Under optimised conditions, good linearity was obtained over 1.0–80.0 or 1.0–120 ng mL⁻¹ with a correlation coefficient (R²) > 0.999. Limits of detection and limits of quantification of the three dyes were 0.28–0.65 and 0.94–2.13 μg kg⁻¹, respectively. The recoveries of the three dyes in shrimp powder, chili powder, tofu sheets, and tomato sauce were in the range of 86.8–119.3%, suggesting that the developed method is a promising tool for accurate quantification of the three dyes at trace levels in foodstuffs.