Development of magnetism-reinforced in-tube solid phase microextraction combined with HPLC for the sensitive quantification of cobalt(II) and nickel (II) in environmental waters

Magnetism-reinforced in-tube solid phase microextraction (MR/IT-SPME) based on porous monolith combined with HPLC/DAD was developed for the sensitive and reliable analysis of cobalt(II) and nickel(II) in environmental waters. Co(II) and Ni(II) were coordinated with 4-(2-pyridylazo)resorcinol (PAR) to form Co-PAR and NiPAR complexes. Monolith-based capillary microextraction column mingled with Fe3O4 nanoparticles (MCN) was tailored according to the chemical properties of Co-PAR and Ni-PAR complexes. To reinforce the extraction performance, a magnetic coil which could produce variable magnetic fields during extraction period was twined round the MCN to set up the MR/IT-SPME system for the efficient extraction of Co-PAR and Ni-PAR complexes. Various parameters influencing the extraction performance were inspected to achieve the most appropriate conditions. Results well proved that the application of magnetic field enhanced the extraction efficiencies of the metal complexes obviously (from 48.4 to 52.2% to 70.9-91.7%). Combing with HPLC with diode array detection (HPLC/DAD), limits of detection for Co(II) and Ni(II) were as low as 0.060-0.14 mu g/L. The suggested MR/IT-SPME-HPLC/DAD approach was successfully applied to measure low concentrations of Co(II) and Ni(II) in different environmental water samples. The recoveries with different fortified levels were in the range of 81.4-118%, and the RSDs for reproducibility varied from 2.0% to 9.7%. Based on the satisfying results, the introduced approach can be used for routine monitoring of Co(II) and Ni(II) in various aqueous environmental samples.