"Fairy dust" electrospray emitters Microcolumn separations and electrospray ionization (ESI) MS seem to be made for each other, with one exception. Capillaries are typically made of an insulating material, such as fused silica, but electrical contact has to be established and maintained for ESI to be successful. To overcome this problem, silica is often coated with a conductive metal, such as gold. Metal coatings on fused silica, however, are physically unstable and typically have a limited lifetime of only a few hours.
intensities of the ions differed. "You need a sharp tip to get a good spray, especially if you have a liquid that has a tendency to wet the outside of the column," says Markides. "The shape of the tip depends on what works best for your application." The "fairy dust" technique proved to be suitable for all emitter shapes and sizes tested. The researchers evaluated the use of the on-column emitters for fast CE separations and found that no obvious band broadening was introduced at the CE/MS interface. "CE is a technique with high resolution and high speed. It is very important that we don't lose this efficiency when we go to the MS detector," says Markides. "We cannot afford to lose anything in the coupling or in the electrospray." Britt Erickson
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"Fairy dust" gold-coated, fused-silica elecrrospray emitter.
In this issue of Analytical Chemistry (p 4115), Karin E. Markides and co-workers at Uppsala University (Sweden) describe a new approach that produces highly stable, sheathless electrospray emitters with unlimited lifetimes. The emitters can even be put directly on microcolumns without any coupling. "We work with LC, CE, and capillary electrochromatography and wanted to have a very convenient, reliable electrospray from microcolumns without any coupling," says Markides. Rather than applying a gold coating by conventional sputtering or electroplating techniques, 2-um gold particles are essentially glued to the capillary tips via a thin film of polyimide. Once the polyimide is cured, the gold particles form an extremely stable layer. "Emitters prepared using this 'fairy dust' technique have provided stable electrospray for over 2000 h and are still operating without any signs of wear," says Markides. The design offers flexibility. "We stabilize the gold onto a fused-silica tip or any other kind of tip," explains Markides. "It doesn't have to be fused silica. We can also apply the gold particles on other types of materials, such as plastics." The approach is therefore not restricted to the bulk material of the column. Several different emitter styles—mechanically shaped, pulled, and unmodified capillary tips—were coated using the "fairy dust" technique. No apparent differences in the sprays were observed; however, the
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Heineman receives Bergen Medal William R Heineman, professor at the University of Cincinnati, was presented with the Torbera Bergman Medal at the 1999 Analysdagarna held in Sweden in June. Heineman was honored for his work in electroanalytical and bioanalytical chemistry. Bergman, a chemistry professor at Uppsala University (Sweden), was one of the foremost chemists in Europe during the later half of the 18th century. The medal is awarded every three years.
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