Novel Cu²⁺-based immobilized metal affinity magnetic nanoparticles for fast magnetic solid-phase extraction of trace...

A novel type of Cu²⁺-based immobilized metal affinity magnetic nanoparticles (MHNTs@PDA@Cu²⁺) was designed and synthesized by a facile and green strategy, and served as an adsorbent for magnetic solid-phase extraction (MSPE) of trace Sudan dyes in foodstuffs. Owing to π-π stacking, hydrogen bonding, hydrophobic and Cu²⁺-azo coordination, MHNTs@PDA@Cu²⁺ possesses superior affinity and very fast adsorption capability to Sudan dyes (adsorption time of 1 min). The main parameters influencing the extraction efficiency of MSPE were investigated and optimized. By coupling MHNTs@PDA@Cu²⁺-based MSPE with HPLC-UV, a simple, fast and sensitive method for the determination of trace Sudan dyes in food samples were developed. Good linearity (R² ≥ 0.9937) and low limits of detection (0.06-0.10 μg L^-1) were obtained. The method was successfully applied to determine Sudan dyes in juice, soy sauce and red wine, and the recoveries for the spiked samples ranged from 78.1% to 112.4% with RSD less than 9.0%.