Microfabricated Devices for Capillary Electrophoresis−Electrospray Mass Spectrometry

Two fundamental approaches for the coupling of microfabricated devices to electrospray mass spectrometry (ESI-MS) have been developed and evaluated. The microdevices, designed for electrophoretic separation, were constructed from glass by standard photolithographic/wet chemical etching techniques. Both approaches integrated sample inlet ports, preconcentration sample loops, the separation channel, and a port for ESI coupling. In one design, a modular, reusable microdevice was coupled to an external subatmospheric electrospray interface using a liquid junction and a fused silica transfer capillary. The transfer capillary allowed the use of an independent electrospray interface as well as fiber optic UV detection. In the second design, a miniaturized pneumatic nebulizer was fabricated as an integral part of the chip, resulting in a very simple device. The on-chip pneumatic nebulizer provided control of the flow of the electrosprayed liquid and minimized the dead volume associated with droplet formation at the electrospray exit port. Thus, the microdevice substituted for a capillary electrophoresis instrument and an electrospray interface--traditionally two independent components. This type of microdevice is simple to fabricate and may thus be developed either as a part of a reusable system or as a disposable cartridge. Both devices were tested on CE separations of angiotensin peptides and a cytochrome c tryptic digest. Several electrolyte systems including a transient isotachophoretic preconcentration step were tested for separation and analysis by an ion trap mass spectrometer.