how to assign conductivity to fluid flow in a microchannel preconcentration modeling?

I am modeling a solution phase preconcentration in microchannel. My system has two inlets and one outlet. From inlet1, buffer (10mM) containing a negatively charged dye is supplied and from inlet2 same buffer (but 100mM) is supplied with syringe pump . When electric field is applied (high voltage at inlet2 with inlet1 grounded ), I am expecting a preconcentration band at the boundary of fluids from two inlets (somewhere close to outlet). For this, I have combined three physics: momentum transport (laminar flow), mass transport (transport of diluted species) and
electric currents.

My question: how to connect/or assign electrical conductivity parameters to particular fluild flow (say from inlet1 and inlet2).

Any help will be appreciated. PS: I am a very beginer of COMSOL and any simulation projects. I am using COMSOL 4.3.