Task specific microextraction column based on monolith for magnetic field-assisted in-tube solid phase microextraction of vanadium species in complex samples prior to online chromatographic analysis

The dominant species of vanadium (V) are V(IV) and V(V) which exhibit different toxicity and biological effects. Thus, speciation of V(IV) and V(V) is highly essential. Efficient sample preparation is the core step in the quantification of V(IV) and V(V). In the present study, a new task specific microextraction column based on monolith mingled with Fe3O4 nanoparticles (MBMC) was in situ synthesized in capillary and utilized as the extraction phase of magnetic field-assisted in-tube solid phase microextraction (MA-IT-SPME) of V(IV) and V(V) species which were coordinated with ethylene diamine tetraacetic acid (EDTA). The prepared MBMC presented porous and superparamagnetic properties, and possessed abundant functional groups. Results revealed that the exertion of magnetic field during adsorption and eluting steps boosted the extraction efficiency of V(IV)-EDTA and V(V)-EDTA chelates from 65.1 % to 55.7 %-90.0 % and 80.1 %, respectively. Under the beneficial extraction parameters, the established MA-IT-SPME was online hyphenated with HPLC/DAD to perform speciation of trace vanadium in water and vegetable samples, the achieved limits of detection were 0.054-0.060 μg/L and 1.4-1.5 μg/kg in water and vegetable samples, respectively, and the spiked recoveries varied from 82.5 to 118 %. In addition, relevant extraction mechanism under magnetic field was explored. In comparison with existing methods, the developed MA-IT-SPME technique displays some attractive merits such as automation, good anti-interference ability, high extraction efficiency, low cost and less use of organic solvent, in the capture of V species. The established online MBMC@MA-IT-SPME-HPLC/DAD system can become a competitive approach for sensitive speciation of V(IV) and V(V) at trace levels in complex samples.

Task specific monolith for magnetic field-reinforced in-tube solid phase microextraction of mercury species in waters prior to online HPLC quantification

In this study, a novel sorbent based on task specific monolith doped with Fe₃O₄ was in situ fabricated in capillary and acted as the extraction medium of magnetic field-reinforced in-tube solid phase microextraction (MFR/IT-SPME) to trap and preconcentrate mercury species which were coordinated with dithizone to form chelates. Various characterization technologies evidenced that the obtained monolithic adsorbent presented porous and super paramagnetic properties, and possessed abundant functional groups. Results evidenced that the implementation of magnetic field during extraction stages enhanced the extraction efficiency of studied Hg chelates from 48.5% to 75.3% to 69.9-94.4%. Under the optimized extraction parameters, the introduced MFR/IT-SPME was online coupled to HPLC/DAD to quantify mercury species at ultra-trace levels in various water samples. Limits of detection varied from 0.0067 μg/L to 0.016 μg/L, and the RSDs for precision were below 7.5%. Additionally, related extraction mechanism was deduced and revealed multiple forces co-contributed to the enrichment. The reliability and accuracy of suggested online approach for speciation analysis of mercury was well proved by confirmatory experiments.