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Science  05 Jul 2002:
Vol. 297, Issue 5578, pp. 15
DOI: 10.1126/science.297.5578.15d

Biological samples often present the challenge of handling a dilute sample in a small (nanoliter) volume; several methods have been developed for concentrating samples before they are introduced into separation columns. For capillary electrophoresis, one simple method is to use field gradients so that all of the analyte moves to one point along a channel. However, the electrodes needed to produce the fields can react with the sample. Ross and Locascio have developed the approach of temperature gradient focusing, which allows for concentration and simultaneous separation of analytes (DNA, proteins, and cells) in solution. A temperature gradient induces an electric field gradient in the solution in the microchannel biased for electrophoresis, and, by opposing the resulting analyte velocity gradient against the bulk flow of fluid, the analyte can be focused. Small analytes in a microfluidic system can be concentrated up to 10,000 times. — PDS

Anal. Chem.74, 2556 (2002).

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