RESUMEN
Chromatographic silica-bonded stationary phases have been prepared using supercritical CO(2) as the reaction medium. (29)Si solid-state NMR spectra of the generated bonded silica phases show unreacted silica species Q(3) and Q(4), alongside important resonances for surface-bound ligands, T(1), T(2), and T(3). Initially, a fluorinated octyl silica (C(8)) phase was produced, by reacting (1)H,(1)H,(2)H,(2)H-perfluorooctyltriethoxysilane with silica particles (3 microm) in sc-CO(2) at 60 degrees C and 450 atm for 3 h. In-house-packed LC columns of this fluorinated sc-C(8) silica phase yielded typical reversed-phase behavior when a standard test mix of benzamide (k' = 1.03), benzophenone (k' = 8.11), and biphenyl (k' = 14.92) was eluted. When packed into fused-silica capillaries for CEC, this fluorinated sc-C(8) silica phase gave linear plots of log k' versus percentage MeOH for benzophenone and biphenyl and, in contrast to octyl or octadecyl silica phases, displayed selectivity for aromatic thioureas when chromatographed among a series of synthetic organic thiourea test solutes. Similarily, an octadecyl silica phase (sc-C(18) silica) was prepared by reaction of n-octadecyltriethoxysilane in sc-CO(2), packed at 9500 psi and examined by LC. The sc-C(18) silica LC column yielded high column efficiency (up to 141 000 N/m (fluorene)) and excellent asymmetry factors (1.06, fluorene) without resource to end-capping. Following a second silylating or end-capping step using hexamethyldisilazane in sc-CO(2), sc-end-capped sc-C(18) silica phases elute N,N-DMA before toluene and the toluidine isomers as a single peak, indicating lowered silanol activity according to the Engelhardt test. A rapid separation of the important pharmaceutical substances, ketoprofen, naproxen, fentoprofen, and ibuprofen, on an sc-end-capped sc-C(18) silica phase is also shown.
RESUMEN
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.