Sacrificial-Site Engineering Enables Enhanced Ion-Interference Resistance in Magnetic Solid-Phase Extraction

Magnetic solid-phase extraction (MSPE) often suffers from significant efficiency loss in high-ionic-strength matrices, where abundant salt ions compress the electrical double layer and compete for adsorption sites, leading to an unstable extraction performance. Here, we report an ion-interference-resistant MSPE strategy that integrates a rationally engineered carbon-based sorbent with an analytical concept of ionic regulation. The sorbent incorporates nitrogen dopants and oxygen vacancy functionalities that act as controllable ion-buffering centers, selectively immobilizing Na⁺ and Cl^- ions to stabilize the interfacial electrostatic environment. Meanwhile, a hydroxyl-enriched surface layer facilitates hydrogen bonding and π-π interactions, ensuring the efficient and selective adsorption of polar analytes such as aflatoxin B₁ (AFB₁). This hierarchical architecture effectively decouples ionic adsorption from target binding, maintaining robust electrostatic microenvironments under saline conditions. The optimized MSPE system retained over 90% of its efficiency at 0.1 mol/L NaCl─approximately a 4-fold improvement in salt tolerance relative to conventional magnetic carbons. When applied to trace detection of AFB₁ in high-salinity food samples (oyster sauce, fermented cheese, and doubanjiang), the method achieved recoveries of 99.7%-108.2% and a detection limit of 16.0 pg/g, far outperforming commercial HPLC sorbents. This work establishes a general methodological framework for ionic regulation in MSPE, offering a robust and practical solution for trace analysis in complex high-salinity matrices.