A novel open-tubular capillary electrochromatography using β-cyclodextrin functionalized graphene oxide-magnetic nanocomposites as tunable stationary phase

Chip-based enantioselective open-tubular capillary electrochromatography (OT-CEC) with β-cyclodextrin (β-CD) conjugated graphene oxide-magnetic nanocomposites (GO/Fe3O4 NCs) as stationary phase was developed. GO/Fe3O4 NCs with high magnetic responsivity, excellent solubility and high dispersibility in water were prepared through a facile and controllable in situ chemical deposition strategy. β-CD was then adsorbed onto the GO/Fe3O4 surface to form GO/Fe3O4/β-CD NCs which were localized to the pre-nominated position in polydimethylsiloxane (PDMS) microchannels with the help of magnets. The resultant GO/Fe3O4/β-CD NCs not only have the magnetism of Fe3O4 NPs that make them easily manipulated by an external magnetic field, but also have the larger surface which can incorporate much more chiral selector molecules. In addition, the successful β-CD decorations endowed GO/Fe3O4/β-CD NCs with excellent wettability and led to enhanced stability against high ionic strength. Compared with the native PDMS microchip, the modified surfaces exhibited more stable and suppressed electroosmotic mobility, and less nonspecific adsorption toward analytes. Successful baseline separation of tryptophan enantiomers was achieved in less than 50 s with a resolution factor of 1.65 utilizing a separation length of 37 mm coupled with in-column amperometric detection. Factors that influence the chiral separation resolution were examined. Under the optimized conditions, the proposed modified chip revealed adequate repeatability concerning run-to-run and day-to-day. These results show that the use of GO/Fe3O4/β-CD NCs within microfluidic channels hold great promise for a variety of analytical schemes.