Electrokinetic control of sample splitting at a channel bifurcation using isotachophoresis

We present a novel method for accurately splitting ionic samples at microchannel bifurcations. We leverage isotachophoresis (ITP) to focus and transport sample through a one-inlet, two-outlet microchannel bifurcation. We actively control the proportion of splitting by controlling potentials at endchannel reservoirs (and thereby controlling the current ratio). We explore the effect of buffer chemistry and local electric field on splitting dynamics and propose and validate a simple Kirchoff-type rule controlling the split ratio. We explore the effects of large applied electric fields on sample splitting and attribute a loss of splitting accuracy to electrohydrodynamic instabilities. We propose a scaling analysis to characterize the onset of this instability. This scaling is potentially useful for other electrokinetic flow problems with self-sharpening interfaces. 1 Author to whom any correspondence should be addressed. New Journal of Physics 11 (2009) 075026 1367-2630/09/075026+15$30.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft