Samples are introduced into the capillary for separation by two different methods. Both having advantages and disadvantages; Electrokinetic injection and Hydrodynamic (Vacuum or Pressure) Injection.
Electrokinetic injection works when the capillary is placed into the catholyte on one end and into the anolyte (containing the sample to be analyzed) on the other end. When a voltage is applied, the EOF moves from the tip of the capillary to the end of the capillary. A siphoning effect occurs, dragging a representative sample into the capillary. Also, ions begin moving into the capillary from the buffer solution due to electrophoretic mobility as part of the sample loading. This can be an advantage when trying to analyze small concentrations of these ions. These injections usually last for 1-5 seconds.