Modification of carbon nanotubes for preconcentration, separation and determination of trace-metal ions

Carbon nanotubes (CNTs) have received much attention for their many potential applications in analytical chemistry due to their adsorptive properties. Unmodified CNTs can be used as sorbents in solid-phase extraction (SPE), especially if metal ions are complexed with an appropriate chelating agent. However, raw CNTs are insoluble and hardly dispersible in solvents due to strong van der Waals interactions that hamper sorption of metal ions. Proper surface treatment of CNTs not only enhances dispersibility but also improves metal sorption and selectivity in SPE. This review focuses on chemical modification of CNTs. We discuss functionalization of CNTs through oxidation and further modification via creation of amide or ester bonds. We also review radical addition with aryl-diazonium salts and the N-2-plasma technique as effective methods of grafting functional groups onto CNT surfaces. Moreover, we present CNT-based composites, including magnetic composites. We show that modified CNTs and their composites can be very attractive as sorbents due to their high adsorption capacity. The review includes several applications of modified CNTs in preconcentration and determination of trace-metal ions in water, food, environmental and biological samples. (C) 2012 Elsevier Ltd. All rights reserved.