A new method is demonstrated which can be used to produce streams of variable, controlled analyte concentration. The method works by electrokinetically manipulating the analyte velocity so that it is different in different parts of a channel. Because of the conservation of charge and mass, the analyte concentration must vary as the inverse of its velocity, so that a spatial variation of the velocity results in a corresponding spatial variation of the concentration. The new dilution method is demonstrated using two different mechanisms for manipulating the analyte electrophoretic velocity. In one demonstration, salt bridges are used to vary the electric potential in the middle of a channel, thereby producing different electrophoretic velocities in the input and output halves of the channel. In the second demonstration, a buffer with a temperature-dependent ionic strength is used, so that the velocity of the analyte is also temperature-dependent, and the output concentration is varied through manipulation of the temperature of the output channel.
Citation: Analytical Chemistry
Pub Type: Journals