Fabrication and characterization of hexahistidine-tagged protein functionalized multi-walled carbon nanotubes for selective solid-phase extraction of Cu2+ and Ni2+

Hexahistidine-tagged protein functionalized multi-walled carbon nanotubes (MWCNTs/6His-tagged protein) were prepared and characterized by ultraviolet–visible spectrophotometry and atomic force microscopy. Both static and dynamical adsorption experiments showed that the MWCNTs/6His-tagged protein served as good sorbent for the solid-phase extraction of Cu2+ and Ni2+. Effective on-line sorption of Cu2+ and Ni2+ on the MWCNTs/6His-tagged protein packed microcolumn was achieved in a pH range of 3.0–4.5 and 4.5–6.0, respectively. The retained Cu2+ and Ni2+ were efficiently eluted with 0.2 mol L−1 imidazole–HCl solution for on-line flame atomic absorption spectrometric determination. The MWCNTs/6His-tagged protein exhibited fairly fast kinetics for the sorption of Cu2+ and Ni2+, and offered up to 20,000 and 1800 times improvement in the tolerable concentrations of co-existing ions over the MWCNTs for solid-phase extraction of Cu2+ and Ni2+, respectively. On-line solid-phase extraction at a flow rate of 5.0 mL min−1 for 60 s gave an enhancement factor of 29 for Cu2+ and 28 for Ni2+, a sample throughput of 45 h−1, and a detection limit (3s) of 0.31 μg L−1 for Cu2+ and 0.63 μg L−1 for Ni2+. The precision for 11 replicate measurements was 2.4% for 10 μg L−1 Cu2+, and 2.5% for 15 μg L−1 Ni2+.