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MEETING NEWS Elizabeth Zubritsky reports from
Pittcon 2004—Chicago, Ill.
CE separations reveal new focusing phenomenon
ied under a microscope for several days, Armstrong says. In these experiments, the researchers saw the same unusual phenomenon that As Dan Armstrong sees it, MS and specthey had noticed even in the earliest work: troscopy have gotten more than their Under the right conditions, the initially share of attention as methods for identidilute samples were focused into compact fying microorganisms. Armstrong, a sepbands as they traveled down the arations specialist at Iowa State capillaries. “Focusing is not new University, has long believed that 0s to capillary electrophoresis,” ArmCE would be a better approach. strong notes. “But there are set So, he has spent the past few 13 s experimental conditions or chemiyears putting the method to its cals you can use to cause them to mettle, showing that it can sepa27 s focus, none of which we used.” rate different types of bacteria, + 38 s – The researchers investigated analyze semen samples for animal the phenomenon further by using husbandry, and most recently, 48 s a homemade CE system with distinguish between two strains CCD imaging. They learned that of E. coli. And in the process, he 74 s they needed the dilute PEO soluand his colleagues have discovtion, a dc electric field, and an ered a new way in which peak electroosmotic flow in a direction sharpening can occur during CE. 0 6 2 4 opposite the movement of the When the researchers began Detection window (cm) microorganisms to induce the this line of inquiry in 1999, CE sample zone compaction. They didn’t have a good track record. Time-resolved photographs showing the compaction of an saw the effect in capillaries as Two other groups had tried it injected sample as it travels down a capillary. (Adapted from large as 100–150 µm i.d. (at but didn’t achieve good efficienAnal. Chem. 2002, 74, 5523–5530). ~200 µm, the heat generated cy, so the approach was discountstarts to lyse the cells), and they predict dye, stained both live and dead cells. ed. But through trial and error, Armthat it should occur in microchannels. Propidium iodide, a red fluorescent strong’s research group eventually hit Armstrong says that part of the effect dye, tended to be rejected by living on a winning combination of experican be attributed to the “hairy particle” cells and, thus, preferentially stained mental parameters, a key part of which model, in which a dilute polymer can addead ones; it also quenched Syto 9, if was adding a very dilute polyethylene sorb and desorb from the surface of the present, so the color coding was clear: oxide (PEO) solution. Such polymers particle, creating a hairy layer. Because Green means alive, red means dead. are commonly used in gels to separate small ions move through these layers “Now, in one run, we [could] separate, DNA, but Armstrong’s group used solumuch more slowly than they move in identify, quantitate, and determine the tions that were 2–3 orders of magnitude free solution, the conductivity—and, percent live and dead bacteria,” Armmore dilute. thus, the field—is altered in this vicinity, strong says. They developed assays to The first application was to diagnose which helps to produce compaction of determine how much active bacteria the two primary culprits of urinary tract the particle injection zone. was present in commercial products infection, Staphylococcus saprophyticus and Shape-induced differential mobility such as dietary supplements containing E. coli (Anal. Chem. 2000, 72, 4474– also contributes, he explains. In this case, Lactobacillus or Bifidobacterium (Anal. 4476). Without sample pretreatment, the the mobilities of nonspherical particles, or Chem. 2001, 73, 4551– 4557). assay exhibited high apparent efficiencies spherical particles that are stuck together, The researchers also applied the and short analysis times of
