Development of a biomarker-driven magnetic separation system: A high-performance and sensitive approach for identifying nicotine-exposed smokers using a task-specific ionic liquid

This work introduces, for the first time, a smart magnetic ionic liquid-based microextraction strategy for direct NCOT determination through hydrophilic-to-magnetic phase conversion without the need for toxic hydrophobic ionic liquids or centrifugation steps. A smart ionic liquid, 1-(3-hydroxybenzyl)-2-methylpyrrolidinium chloride ([HMP][Cl]), was rationally designed according to the structural characteristics of NCOT to improve extraction selectivity and efficiency. The synthesized ionic liquid was characterized using NMR, FTIR, UV–Vis, and CHN analyses. DFT calculations and UV–Vis studies confirmed the formation of the NCOT–[HMP][Cl] complex through cooperative intermolecular interactions. Following extraction, the complex was magnetically transformed, enabling rapid separation from the aqueous phase using an external magnet without centrifugation. The developed method exhibited excellent analytical performance, including a limit of detection of 0.10 ng/mL, a limit of quantification of 0.19 ng/mL, and a linear dynamic range of 1.0–300 ng/mL. Good precision was achieved with intra-day and inter-day RSD values of 1.6% and 2.7%, respectively. Application of the method to urine and environmental water samples provided recoveries ranging from 98.1% to 99.9%, confirming the reliability and applicability of the proposed approach.