Microfabricated isoelectric focusing device for direct electrospray ionization-mass spectrometry

A novel microfabricated device for isoelectric focusing (IEF) incorporating an optimized electrospray ionization (ESI) tip was constructed on polycarb onate plates using laser micromachining. The IEF microchip incorporated a s eparation channel (50 mu x 30 mu x 16 cm), three fluid connectors, and two buffer reservoirs. Electrical potentials used for IEF focusing and electros pray were applied through platinum electrodes placed in the buffer reservoi rs, which were isolated from the separation channel by porous membranes. Di rect ESI-mass spectrometry (MS) using electrosprays produced directly from a sharp emitter "tip" on the microchip was evaluated. The results indicated that this design can produce a stable electrospray and that performance wa s further improved and made more flexible with the assistance of a sheath g as and sheath liquid. Error analysis of the spectral data showed that the s tandard deviation in signal intensity for an analyte peak was less than sim ilar to 5% over 3 h. The production of stable electrosprays directly from m icrochip IEF device represents a step towards easily fabricated microanalyt ical devices. Microchannel IEF separations of protein mixtures were demonst rated for uncoated polycarbonate microchips. Direct microchannel IEF-ESI-MS was demonstrated using the microfabricated chip with an ion-trap mass spec trometer for characterization of protein mixtures.