Electroosmotic flow-balanced isotachophoretic stacking with continuous electrokinetic injection for the concentration of anions in high conductivity samples

An EOF counter-balanced ITP boundary has been used to stack anions from high conductivity samples during continuous electrokinetic injection of the sample. In a polystyrenesulfonate/poly(diallyldimethylammonium chloride) polyelectrolyte coated capillary, the time at which the ITP boundary exited the capillary could be prolonged by balancing the movement of the boundary with the EOF. Using a bis-tris-propane electrolyte, the ITP boundary was removed from the capillary within 7 min, while when using triethanolamine the ITP boundary was still at 30% of the capillary after 2 h of injection. Using these systems, the sensitivity of a mixture of simple organic acids in 100 mM Cl⁻ was improved by 700–800-fold using bis-tris-propane with a whole-capillary injection of the sample and 5 min of electrokinetic injection at +28 kV, and 1100–1300-fold using triethanolamine and 60 min of electrokinetic injection under the same conditions. The potential of the method to be applicable to high conductivity samples was demonstrated by stacking a whole capillary filled with urine spiked with naphthalenedisulfonic acid, with limits of detection 450 times lower than those achievable with a normal hydrodynamic injection.