1 research outputs found
(Almost) Stationary Isotachophoretic Concentration Boundary in a Nanofluidic Channel Using Charge Inversion
The
present work is an experimental study of a new means to induce
a quasi-stationary boundary for concentration or separation in a nanochannel
induced by charge inversion. Instead of using pressure-driven counter-flow
to keep the front stationary, we exploit charge inversion by a highly
charged electrolyte, RuÂ(bpy)<sub>3</sub>Cl<sub>2</sub>, that changes
the sign of the zeta potential in part of the channel from negative
to positive. Having a non-charge inverting electrolyte (MgCl<sub>2</sub>) in the other part of the channel and applying an electric field
can create a standing front at the interface between them without
added dispersion due to an externally applied pressure-driven counterflow.
The resulting slow moving front position can be easily imaged optically
since RuÂ(bpy)<sub>3</sub>Cl<sub>2</sub> is fluorescent. A simple analytical
model for the velocity field and front axial position that reproduces
the experimental location of the front shows that the location can
be tuned by changing the concentration of the electrolytes (and thus
local zeta potential). Both of these give the charge inversion-mediated
boundary significant advantages over current methods of concentration
and separation and the method is, therefore, of particular importance
to chemical and biochemical analysis systems such as chromatography
and separations and for enhancing the stacking performance of field
amplified sample injection and isotachophoresis. By choosing a non-charge
inverting electrolyte other than MgCl<sub>2</sub>, either this electrolyte
or the RuÂ(bpy)<sub>3</sub>Cl<sub>2</sub> solution can be made to be
the leading or trailing electrolyte