Solid Phase (Micro)extraction Tools Based on Carbon Nanotubes and Related Nanostructures

Abstract

The evolution of Analytical Sciences has been marked by several turning points which have changed the analytical laboratories. They have defined a variety of stages dominated by one or two key trends in Analytical Chemistry with clear influence in the “products” yielded in those years. This evolution started with the massive use of instruments in 1950s and continues with the growing importance of miniaturization and simplification in recent years. Nowadays, the analytical trends are also influenced by the development in other scientific and technological areas. Concretely, nanotechnology can be considered as a new, increasingly important trend in science in general and in analytical chemistry in particular. The outstanding properties of the nanoparticles and nanostructured materials have opening up a wide variety of challenging possibilities in this area. It should be expected that the evolution of this analytical trend will be markedly affected by the nanotechnological developments. Nowadays there are a large variety of nanoparticles commercially available or easily synthesizable in the laboratory such as gold nanoparticles, quantum dots and carbon nanoparticles, among others. Carbon nanotubes (CNTs) have received special research attention since their discovery on account of their unique and outstanding properties which results in a wide variety of applications in different scientific and technological areas. Carbon nanotubes can be considered as a graphene sheet that has been rolled up to form as extended tube-like structures (Harris, 1999). They range between a few tens of nanometers and several micrometers in length with an outer diameter from ca. 2.5 to 30 nm. They can consist of a single graphene sheet (singlewalled carbon nanotubes, SWCNTs) or a series of concentric layers (multiwalled carbon nanotubes, MWCNTs). Since their discovery in 1991 by Iijima (Iijima, 1991), carbon nanotubes have been the target of theoretical and practical research with the aim of dilucidating their outstanding properties at the nanoscale level. The main difficult in this context is the marked tendency to aggregation of this nanomaterial, which makes difficult to distinguish between supramolecular assemblies and isolated carbon nanotubes properties. Apart from their thermal stability, excellent mechanical and electric properties, as well as their highest tensile 22