Capillary Zone Electrophoresis−Electrospray Mass Spectrometry at Submicroliter Flow Rates: Practical Considerations and Analytical Performance

A novel method for the production of coated capillaries for capillary zone electrophoresis−electrospray mass spectrometry (CZE−ESMS), operating at 100−200 nL/min flow rates is described. Electrophoretic conditions conducive to the simultaneous operation of ESMS were investigated for microsprayers of different inner diameters. The ruggedness and reliability of the CZE columns with microsprayers of 20 μm i.d. were investigated over 6 h of uninterrupted operation. Detection limits in the order of 0.1−5 fmol were obtained for peptide standards of molecular masses ranging from 500 to 2500 Da, and sensitivity was ∼10 times higher than that achieved using the more conventional sheath flow CZE−ESMS interface. Such enhancement of signal detectability provided distinct advantages for on-line line tandem mass spectrometric analyses whereby structurally informative MS−MS spectra were obtained using femtomole loadings of peptides and glycopeptides from ovalbumin digests.