A new Fe3O4-MWCNTs-reinforced hollow fiber solid/liquid phase microextraction-based natural deep eutectic solvent for determination of trace phthalate esters in aqueous samples using HPLC–DAD

Herein, we present a new eco-friendly microextraction method based on the magnetite/multi-walled carbon nanotubes reinforced and natural deep eutectic-filled hollow fiber solid/liquid phase microextraction, abbreviated as HF-SLPME, combined with HPLC–DAD analysis. This method has been developed to determine trace levels of phthalate esters, including diethyl phthalate, benzyl butyl phthalate, and di-iso-butyl phthalate in urine, blood plasma, tap water, and groundwater samples. The natural deep eutectic solvents were prepared using terpenoid-derived natural compounds containing menthol and camphor in various ratios. The HF-SLPME device was constructed by reinforcing and immobilizing the synthesized Fe₃O₄-MWCNTs within the pores of a 2.5 cm segment of hollow fiber microtube through ultrasonication, followed by filling the lumen with the natural deep eutectic solvent with both ends heat sealing. The extraction process was conducted in direct immersion mode. Values of crucial variables for HF-SLPME were optimized through a multivariate methodology based on a central composite design, with 30 extraction tests performed to determine the best conditions. The method exhibited good linearity (correlation coefficients R² > 0.996) over a dynamic range lower than 0.927–10³ µg L⁻¹. The results show that the limits of detection/quantification for the chosen PEs ranged from 0.19 to 0.27/ 0.65 to 0.92 µg L⁻¹ with enrichment factor˃ 37.24. As evidenced by intra- and inter-day precisions, satisfactory reproducibility was achieved with relative standard deviations (RSDs) below 3.7% and 5.1%, respectively. The recoveries of the selected phthalate esters from spiked real samples ranged from 88.4 to 111.1%, with relative standard deviations between 2.3 and 6.5%. This HF-SLPME-HPLC–DAD method offered a new, cost-effective, sensitive microextraction approach for determining and quantifying phthalate esters in aqueous samples with complex matrices.