Highly sensitive analysis of catecholamines by counter-flow electrokinetic supercharging in the constant voltage mode.

Electrokinetic supercharging is one of the most powerful sample-stacking methods that combines field amplified sample injection and transient ITP. In counter-flow electrokinetic supercharging, a constant counter pressure is applied during sample injection in order to counterbalance the movement of the injected sample zone. As a result, there will be a pronounced increase in the amount of sample injected and the portion of the capillary available for electrophoresis. In this report, counter-flow electrokinetic supercharging optimization factors such as the electric field application in the constant voltage and constant current modes, the magnitude of counter pressure, and the terminating electrolyte concentrations were investigated. The enrichments obtained with a 30 min injection of 10 nM catecholamines in 5 mM terminating electrolyte solution in the constant voltage mode applying a counter pressure of 1.3 psi were 41,000-fold for dopamine, 50,000-fold for norepinephrine, and 32,000-fold for epinephrine, yielding detection limits of 1.3, 1.4, and 1.2 nM, respectively, with absorbance detection at 200 nm.