Chain-Length dependent IL@MWCNTs adsorbents for solid-phase extraction of aflatoxin B1: Enhancing oil-matrix...

Edible oils are prone to contamination by aflatoxin B₁ (AFB₁), posing significant food safety risks. In this study, a series of imidazolium ionic liquids (ILs) with varying alkyl chain lengths (C₂, C₄, C₆, C₈) were covalently grafted onto multi-walled carbon nanotubes (MWCNTs) via a free-radical method to develop IL@MWCNT adsorbents (EMIM@MWCNT, BMIM@MWCNT, HMIM@MWCNT, OMIM@MWCNT) for solid-phase extraction (SPE) of AFB₁, followed by HPLC-fluorescence detection. Comprehensive characterization revealed that chain length critically influenced material properties: SEM and BET analysis demonstrated that HMIM@MWCNT (C₆) exhibited the highest specific surface area (101.6 m²/g) and optimal pore diameter (35.64 nm), while contact angle measurements and dispersion tests in non-polar solvents highlighted its superior hydrophobicity and oil-matrix compatibility. FTIR and XPS confirmed covalent IL grafting and the presence of oxygenated groups (hydroxyl, epoxy), which facilitated π-π stacking, hydrogen bonding, and electrostatic interactions with AFB₁. Adsorption studies indicated that HMIM@MWCNT achieved the fastest kinetics (equilibrium within 20 min) and highest capacity (45.2 mg/g), following pseudo-second-order kinetics and Freundlich isotherm models. The C₆ chain length balanced hydrophobicity and steric effects, enhancing AFB₁ affinity compared to shorter chains (C₂, C₄) and mitigating aggregation observed with longer chains (C₈). The optimized SPE-HPLC method demonstrated a wide linear range (0.5 μg/L-500 μg/L, R² = 0.9997), ultra-low detection limit (0.1 μg/L), and satisfactory recoveries (88.0-104%) in spiked corn oil with RSD ≤6.0%. The adsorbent retained >98% efficiency over five cycles, underscoring its reusability. This work elucidates the role of IL alkyl chain length in tailoring adsorbent properties for efficient AFB₁ extraction, offering a robust strategy for mycotoxin monitoring in lipid-rich matrices.