Electrokinetic Dispersion in Field Amplified Sample Stacking

In this work, we performed an experimental study of electrohydrodynamic effects on the dispersion of sample ions in field amplified sample stacking (FASS). A typical FASS experiment involves a streamwise electrical conductivity gradient collinear to the applied electric field to enhance the sample stacking. Earlier studies on FASS have focused on how the conductivity gradient sets a non-uniform electro-osmotic flow which causes the dispersion. However, the coupling of the electric field with conductivity gradient leads to a destabilizing electric body force and generates unstable flow. This work demonstrates that generated body force influences the dynamics of FASS. We present a scaling analysis to show that at high fields, electrohydrodynamic effects play a vital role in sample dispersion. To justify our scaling arguments, we performed experiments at varied electric fields which shows that at high electric fields maximum concentration enhancement is lowered significantly. To ensure the EHD effects on the dynamics of FASS, we have also performed experiments with suppressed EOF conditions.