A modular subatmospheric electrospray interface with fiber optic UV detection close to the electrospray tip was developed for coupling of microcolumn separation techniques with mass spectrometry. The interface was based on a liquid junction with a removable microelectrospray tip. The electrospray tip was enclosed in a subatmospheric chamber attached in front of the sampling orifice of the mass spectrometer. The inlet of the liquid junction was maintained at atmospheric pressure, and thus no pressure drop developed across the separation column. The flow rate of the electrosprayed liquid from the liquid junction reservoir was adjusted by the pressure in the electrospray chamber. In this approach, a continuous and stable electrospray could be achieved without the use of an external pump. Since the electrospray did not depend on fluid delivery from the separation column, coated capillaries without electroosmotic flow as well as capillaries with electroosmotic flow could be used for capillary electrophoresis. In addition, the interface was found to be effective with capillary liquid chromatography. The use of a fiber optic UV detector placed close to the exit of the separation column provided additional detection information and a simple means of troubleshooting. The interface did not significantly influence the quality of the separation, even with columns generating several hundred thousand theoretical plates. Peptide samples in the submicromolar concentration range were detected, corresponding to a limit of detection in the attomole range.