Carbon nanotubes as separation carrier in capillary electrophoresis

Abstract

The utility and versatility of carboxylic single-walled carbon nanotubes (c-SWNT) in capillary electrophoresis (CE) is demonstrated, using as model solutes homologues and structural isomers. In the case of homologues of caffeine and theobromine, distinct changes in the electrophoretic parameters occur at a critical concentration of c-SWNT in the run buffer. It is suggested that the c-SWNT of a definite concentration could form a network in the run buffer as a pseudostationary phase on the basis of the unique tubule structure, providing a different separation from sodium dodecyl sulfate (SDS) micelles. In the case of structural isomers of catechol and hydroquinone, differing from the homologues, it is mainly attributable to the functional groups on the c-SWNT that have an effect on the electrophoretic behaviors by forming intermolecular hydrogen bonding with analytes. Furthermore, aggregated c-SWNT serve as anticonvective media and minimize solute diffusion contributing to zone broadening. The presence of charged c-SWNT suppressed the electrodiffusion and decreased the adsorption between capillary wall and solutes, which led to better peak shapes of isomers.

Application of Carbon Nanotubes in Chiral and Achiral Separations of Pharmaceuticals, Biologics and Chemicals

“…Although β-CD has been also added to the surface of other nanoparticles such as polystyrene, Al2O3 and TiO2, the best separation of clenbuterol was achieved by MWCNTs-β-cylodextrin ( Figure 2) [48]. It is the unique structure of CNTs with very large surface areas and its good dispersion in the presence of a surfactant that enhances enantioseparations [49,76]. MWCNTs can also be used to quantify the amount of clenbuterol in urine and blood samples to test for any potential abuse of the use of the drug.…”

“…Several examples with promising outcomes have been reported where SWCNTs and MWCNTs were tested for their abilities to achieve achiral separations (Table 2) [49,50,52,53,76]. For example, the analysis of catecholamine in blood is important for monitoring the normal and pathological activity of the adrenal gland [131,132].…”

“…Caffeine has an additional methyl group than theobromine that retards its movement resulting in a longer retention time [76]. It is believed that the presence of c-SWCNTs in the buffer solution offers additional interaction sites with the analytes by forming an aggregation like a network with high surface area and molecular sieving properties [76].…”

“…The mechanism of action of c-SWCNTs in the separation process, however, has been shown to be independent of the micelle formation with surfactants (1% w/w) SDS. When SDS 1% (w/w) (which doesn't form the micelle network) was used in the buffer medium in the absence of c-SWCNTs, the separation of theobromine and caffeine did not occur [76]. Increasing the migration time due to the network-like structure formed by c-SWCNTs, improves the separation of theobromine and caffeine.…”

Applications of nanomaterials in liquid chromatography: Opportunities for separation with high efficiency and selectivity

“…Thus, MS, fluorescence detection, and partial filling techniques are generally used to overcome these adverse effects [17,18]. Use of carbon allotropes, such as fullerene and carbon nanotubes, as separation media in MEKC [19,20], open tubular CEC [21], and monolithic CEC [22] with excellent performance has recently been reported.…”