Capillary electrophoresis (CE) provides high performance separation but suffers from the low sensitivity for widely used absorbance detection due to the short optical pathlength of a capillary. Because of this, many stacking and extraction technique has been developed. Counter-flow (CF) electrokinetic supercharging (EKS) is one of the technique to enhance the detection sensitivity. This method provides easy and efficient analyzing method without additional detecting devices.
CF-EKS is a method which combines some different sample concentration methods. Electrokinetic supercharging (EKS) is combined with field amplified sample injection (FASI) and transient isotachophoresis (tITP), and CF-EKS is adding counter flow at EKS that help to inject and separation.
TITP is one of sample stacking techniques using difference of ion mobilites, which binds isotachophoresis with zone electrophoresis (CZE). ITP is just stacking technique, not separate. For separate this, use LE after TE that makes continuously CZE. Leading electrolyte (LE) has high mobility. In contrast, terminating electrolyte (TE) has low mobility. As a result, there become difference of mobility, sample is compressed between LE and TE. Sample stacking will continue until LE passing through TE. Then samples are separated.
FASI uses electric field difference caused by conductivity difference. After filling the whole capillary with run buffer and low conductivity sample with electrokinetic injection (EKI). Sample stacked at the boundary of sample and run buffer because of high electric field occurred at the injection point.
EKS is improved sample stacking technique using FASI with tITP. LE has high conductivity but TE and sample zone has low conductivity. That makes high electric field in electrolyte boundary. And this difference makes sample stacked in electrolyte boundary.
One limitation of EKS is that the portion of the capillary length filled by FASI should not go beyond the point of allowing acceptable separation for the subsequent tITP.
Counter Flow Electrokinetic Supercharging (CF-EKS) is simple improvement of EKS.
CF-EKS uses a counter pressure to counterbalance the movement of the stacked sample zone during injection. This counter flow makes stop the electrolyte boundary near inlet of capillary. By this, we can inject much more and sufficient separation length
CF-EKS strong point is no need to sample preparation step, not much effected by sample ionic strength, provides easy and efficient analyzing method without any additional device. And it has low cost and high sensitivity. And more, it can be applicability to various samples.