Periodic magnetic actuation-assisted microfluidic enrichment for online HPLC–MS/MS determination of multiclass veterinary drug residues in aquaculture water

Sensitive determination of multiclass veterinary drug residues in aquaculture water requires efficient sample preparation capable of handling trace contaminants while minimizing sample consumption and manual operation. Here, a periodic magnetic actuation-assisted microfluidic enrichment platform was integrated online with HPLC–MS/MS for the determination of quinolones, sulfonamides, tetracyclines, and malachite green. Fe₃O₄@GO was magnetically confined within a multi-serpentine microchannel, and the effects of channel geometry and magnetic operating conditions on sorbent retention and flow-through capture were systematically evaluated. The multi-serpentine configuration limited Fe₃O₄@GO loss to 3.82% after ten operating cycles, while 200 mT and 10 Hz provided effective magnetic confinement and capture performance. In the final workflow, 50 μL of sample was loaded at 5 μL min⁻¹ for 10 min, followed by mobile-phase-mediated release and transfer through an online C 18 cleanup/trapping column for chromatographic analysis. The method achieved limits of detection of 0.02–0.17 μg L⁻¹, limits of quantification of 0.07–0.53 μg L⁻¹, recoveries of 79.84–97.66% in spiked real aquaculture water, and RSDs of 3.41–7.24%. These results demonstrate a low-volume and integrated sample-preparation strategy for multiclass veterinary drug determination in aquaculture-water matrices.