An atmospheric ion lens incorporated into an electrospray ion source for capillary electrophoresis-mass spectrometry (CE-MS) is found to extend the stable operational regions for both flow rates and electrospray ionization (ESI) voltages. The stable operating conditions for the ESI source with and without the ion lens were characterized. The results showed that the stable operation region was widest when the voltage difference between the sprayer and the ion lens ranges from 2.6 to 2.8 kV, and under these condition, the CE-MS interface can be adapted to a broader range of electroosmotic and modifier flow rates. Modeling of the electric field in the electrospray ion source with the ion lens suggests that the extension of the stable region is attributed to the flatter equipotential surfaces around the sprayer tip and higher electric field strengths in the rest of the interface region.