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 Cu(2+) and Ni(2+). Effective on-line sorption of Cu(2+) and Ni(2+) 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 Cu(2+) and Ni(2+) were efficiently eluted with 0.2mol 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 Cu(2+) and Ni(2+), 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 Cu(2+) and Ni(2+), respectively. On-line solid-phase extraction at a flow rate of 5.0 mL min(-1) for 60s gave an enhancement factor of 29 for Cu(2+) and 28 for Ni(2+), a sample throughput of 45 h(-1), and a detection limit (3s) of 0.31 microg L(-1) for Cu(2+) and 0.63 microg L(-1) for Ni(2+). The precision for 11 replicate measurements was 2.4% for 10 microg L(-1) Cu(2+), and 2.5% for 15 microg L(-1) Ni(2+).