A CE ESI-MS INTERFACE FOR STABLE, LOW-FLOW OPERATION/

A ragged, stable liquid sheath interfacing procedure for on-line CE/IM S is described, This procedure combines optimized component sizes, tap ered capillary tips, and adjustment of the capillary with respect to t he liquid sheath tube during electrospray operation (active capillary positioning) to establish a stable electrospray quickly and reliably. The interface is especially effective at low flow rates, and CE/MS wit h a liquid sheath now rate of 250 nL/min has been achieved, Active cap illary positioning also allows on-line capillary isoelectric focusing mass spectrometry with in-probe focusing. In this application, the cap illary is retracted into the liquid sheath tube, which becomes a micro reservoir. After focusing the capillary is returned to its proper posi tion for electrospray, and focused zones are mobilized into the mass s pectrometer for on-line detection. Both active capillary positioning a nd in-probe focusing readily lend themselves to automation.