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.

Self-aligning subatmospheric hybrid liquid junction electrospray interface for capillary electrophoresis.

We report a construction of a self-aligning subatmospheric hybrid liquid junction electrospray interface for CE eliminating the need for manual adjustment by guiding the capillaries in a microfabricated liquid junction glass chip at a defined angle. Both the ESI and separation capillaries are inserted into the microfabricated part until their ends touch. The distance between the capillary openings is defined by the angle between the capillaries. The microfabricated part contains channels for placement of the capillaries and connection of the external electrode reservoirs. It was fabricated using standard photolithographic/wet chemical etching techniques followed by thermal bonding. The liquid junction is connected to a subatmospheric electrospray chamber inducing the flow inside the ESI needle and helping the ion transport via aerodynamic focusing.

Simulations of high-Q optical nanocavities with a gradual 1D bandgap.

High-quality cavities in hybrid material systems have various interesting applications. We perform a comprehensive modeling comparison on such a design, where confinement in the III-V material is provided by gradual photonic crystal tuning, a recently proposed method offering strong resonances. The III-V cavity couples to an underlying silicon waveguide. We report on the device properties using four simulation methods: finite-difference time-domain (FDTD), finite-element method (FEM), bidirectional eigenmode propagation (BEP) and aperiodic rigorous coupled wave analysis (aRCWA). We explain the major confinement and coupling effects, consistent with the simulation results. E.g. for strong waveguide coupling, we find quantitative discrepancies between the methods, which establishes the proposed high-index-contrast, lossy, 3D structure as a challenging modeling benchmark.