Fabrication and characterization of hexahistidine-tagged protein functionalized multi-walled carbon nanotubes for selective solid-phase extraction of Cu 2+ and Ni 2+

Abstract

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 0.2 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 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 60 s 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 (3 s) of 0.31 μg L −1 for Cu 2+ and 0.63 μg L −1 for Ni 2+. The precision for 11 replicate measurements was 2.4% for 10 μg L −1 Cu 2+, and 2.5% for 15 μg L −1 Ni 2+.