Capillary zone electrophoresis (CZE) was employed to separate sugars according to their electrophoretic mobilities In strong alkaline solutions (pH ca. 13). Saccharide zones were monitored electrochemlcally using amperometric detection at a constant potential, 0.6 V (vs Ag/AgCI), with a cylindrical copper wire electrode (25 pm In diameter). The Cu-wlre microelectrode In strong basic solutions had electrochemical behavior similar to that of Cu electrodes with larger dimensions and appeared to show no deterioration for hundreds of runs. A sample mixture containing 15 different sugars was separated In less than 45 min with separation efficiencies up to 200 000 theoretical plates. The calibration plot was found to be linear over 3 orders of magnitude and the limits of detection for the saccharides studied were In the femtomole range.

Electrochromatography is utilized to separate a mixture of 16 different polycyclic aromatic hydrocarbons (PAHs). Fused-silica capillary columns ranging in size from 50 to 150 µ i.d. were packed (20-40-cm sections) with 3•µ octadecylsilica particles. A potential of 15-30 kV is applied across the 30-50-cm total length capillary column to generate electroosmotic flow that carries the PAHs through the stationary phase. An intracavity-doubled argon ion laser operating at 257 nm is used to detect the PAHs by laser-induced fluorescence. Efficiencies up to

In analogy to pressure-driven gradient techniques in high-performance liquid chromatography, a system has been developed for delivering electroosmotically driven solvent gradients for capillary electrochromatography (CEC). Dynamic gradients with submicroliter per minute flow rates are generated by merging two electroosmotic flows that are regulated by computer-controlled voltages. These flows are delivered by two fused-silica capillary arms attached to a T-connector, where they mix and then flow into a capillary column that has been electrokinetically packed with 3-μm reversed-phase particles. The inlet of one capillary arm is placed in a solution reservoir containing one mobile phase, and the inlet of the other is placed in a second reservoir containing a second mobile phase. Two independent computer-controlled, programmable, high-voltage power supplies (0−50 kV)one providing an increasing ramp and the other providing a decreasing rampare used to apply variable high-voltage potentials to the mobile phase reservoirs to regulate the electroosmotic flow in each arm. The ratio of the electroosmotic flow rates between the two arms is changed with time according to the computer-controlled voltages to deliver the required gradient profile to the separation column. Experiments were performed to confirm the composition of the mobile phase during a gradient run and to determine the change of the composition in response to the programmed voltage profile. To demonstrate the performance of electroosmotically driven gradient elution in CEC, a mixture of 16 polycyclic aromatic hydrocarbons was separated in less than 90 min. This gradient technique is expected to be well-suited for generating not only solvent gradients in CEC but also other types of gradients, such as pH and ionic strength gradients, in capillary electrokinetic separations and analyses.

No abstract

Capillary electrophoresis with UV-laser-excited native fluorescence has been employed for ultrasensitive determination of polycyclic aromatic hydrocarbons, including anthracene, phenanthrene, benz[a]anthracene, methylanthracene, pyrene, fluoranthene, and perylene. The separation is based on solvophobic association of the analytes with tetraalkylammonium ions in mixed acetonitrile/water solvent. With both near-UV (325-nm) and deep-UV (257-nm) laser excitation, background fluorescence from the fused silica capillary and the nonaqueous electrolyte was the limiting factor in detection sensitivity. Effective rejection of the intense capillary wall fluorescence was achieved by the use of a high-numericalaperture microscope objective coupled with an adjustable precision slit in a confocal configuration. The achieved mass detection limits were in the range of (3-15) X 10"20 mol, with linear fluorescence response spanning over 4 orders of magnitude. This sensitivity is expected to be sufficient for analyzing chemical carcinogens, anticancer drugs, and their metabolites in individual mammalian cells.