Microfabricated liquid junction hybrid capillary electrophoresis-mass spectrometry interface for fully automated operation.

One of the challenging instrumental aspects in coupling an automated CE instrument with ESI mass spectrometry (CE-MS) is finding the balance between the stability, reproducibility and sensitivity of the analysis and compatibility with the standard CE instrumentation. Here, we present a development of a new liquid junction based electrospray interface for automated CE-MS, with a focus on the technical design followed by computer modeling of transport conditions as well as characterization of basic performance of the interface. This hybrid arrangement designed as a microfabricated unit attachable to the automated CE instrument allows using of a wide range of separation capillaries with respect to their diameter, length or internal coating (e.g., for suppressed electroosmotic flow). Different compositions of the ESI liquid and background electrolyte solutions can be used if needed. The microfabricated part, prepared by laser machining from polyimide, includes a self-aligning liquid junction, a short transport channel, and a pointed sprayer for the electrospray ionization. This microfabricated part is positioned in a plastic connection block securing the separation capillary and flushing ports. Transport conditions were modelled using computer simulation and the real life performance of the interface was compared to that of a commercial sheath liquid interface. The basic performance of the interface was demonstrated by separations of peptides, proteins, and oligosaccharides.