Alkylthiol gold nanoparticles in open-tubular capillary electrochromatography

Open-tubular columns for capillary electrochromatography (CEC) were formed by immobilising dodecanethiol gold nanoparticles on prederivatised 3-aminopropyl-trimethoxysilane (APTMS) or 3-mercaptopropyl-trimethoxysilane (MPTMS) fused-silica capillaries. The initial stage of this research involved the synthesis and characterisation of dodecanethiol gold nanoparticles, with tunnelling electron microscopy analysis of the dispersed phase of the gold nanoparticles dispersion in CHCl₃ revealing spherical particles. The surface features of an Au-MPTMS coated capillary column were determined using scanning electron microscopy. The electroosmotic flow characteristics of Au-APTMS and Au-MPTMS capillary columns were then determined, by varying the pH and the voltage. The electrochromatographic properties of the gold nanoparticles CEC capillaries were investigated using a "reversed-phase" test mixture of thiourea, benzophenone and biphenyl and selected pyrethroid pesticides. Efficient separations of benzophenone and biphenyl solutes on Au-MPTMS and Au-APTMS capillary columns were obtained, as were linear plots of logarithm capacity factor versus % MeOH. A study of the reproducibility of retention for these solutes on Au-APTMS, Au-MPTMS and on a loosely coated capillary demonstrated the necessity of a coupling agent to prevent the gold nanoparticles from washing-off. These dodecanethiol gold capillary columns are easier to produce and operate than packed capillary columns. The research work confirms the use of gold nanoparticles as a novel phase for open-tubular CEC, demonstrating reproducible retention and characteristic reversed-phase behaviour.