Magnetic solid-phase extraction using metal–organic framework-based biosorbent followed by ligandless deep-eutectic solvent-ultrasounds-assisted dispersive liquid–liquid microextraction (DES-USA-DLLME) for preconcentration of mercury (II)

Abstract

A novel magnetic biosorbent was prepared for preconcentration and extraction of Hg (II). Magnetic nanoparticles (Fe3O4@SiO2-NH2) were deposited on a metal–organic framework (HKUST-1). It was used as a proper platform for immobilization of a thymine-rich aptamer (Apt-Fe3O4@SiO2-NH2@HKUST-1). Characterization of the biosorbent was performed by various methods (XRD, FT-IR, SEM, and TGA). Mixing of biosorbent with the sample solution resulted in efficient selective binding of Hg (II) to Apt-Fe3O4- SiO2-NH2@HKUST-1. After separation with a magnet and then releasing Hg (II), further preconcentration was carried out by dispersive liquid–liquid microextraction (DLLME). In this step, a hydrophobic and low density deep – eutectic solvent (DES-1, l-menthol and salicylic acid in a molar ratio of 4:1) was used as extractant and complexing agent for Hg (II). Ultrasound bath was used for efficient dispersion of DES-1 in sample solution. After centrifugation and phase separation, DES-rich phase was introduced to an electrothermal atomic absorption spectrometer for determination of Hg (II) at 253.7 nm. An unprecedented enrichment factor (EF) of about 2400 was obtained by the proposed procedure. Under the optimized conditions, the dynamic linear range of 2–120 µg L−1 (R2 = 0.998). Limit of detection (LOD) and limit of quantification (LOQ) for Hg (II) were 0.34 ng mL−1 and 1.13 ng mL−1, respectively. Intra- and inter-day precision of the method were calculated (3.68% and 3.80%, respectively) for the determination of 1.0 µg L−1 of Hg (II) as relative standard deviation (RSD%). The sorbent capacity (Qe) was 156 µg mL−1 Hg (II). The proposed procedure was successfully applied to the determination of trace amounts of Hg (II) in several real samples.