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Optimal Nanospray Interfaces for Coupling Capillary Electrophoresis to Mass Spectrometry

Technology #017-003-nemes

Researchers at the George Washington University developed an ultrasensitive, robust CE-nanoESI (capillary electrophoresis-nano-flow electrospray ionization) interface for MS (mass spectroscopy) that enables the discovery and characterization of proteins in as little as 1 ng of protein digest. This sensitivity means that proteomics no longer requires large tissue amounts containing a large amount of cell heterogeneity, but can be carried out on a handful, or even single, cells.

Capillary Electrophoresis (CE) works well for separating even small mass spectrometry samples efficiently, but its power is limited due to difficulty ionizing the separated molecules. Electrospray ionization (ESI) provides excellent ionization of samples, but is a technical challenge to combine with CE, because the required sheath fluid dilutes the samples. Nano-flow ESI minimizes sample dilution, unlocking the power of CE for truly minute samples.

This design uses a small-bore tapered-tip metal emitter to integrate the CE separation capillary into a nanoESI source via a co-axial sheath-flow configuration (200–350 nL/min sheath liquid). The device provides an estimated 260 zmol lower limit of detection, or 156,000 copies for peptide standards. Compared with other co-axial sheath-flow interfaces, this sensitivity is ~4000-times higher than those based on large-bore emitters. Similar sensitivity has been achieved with borosilicate capillary nanoESI interfaces. However, borosilicate capillaries are susceptible to clogging and require dangerous hydrofluoric acid in the manufacturing process. Conversely, our small-bore tapered-tip metal emitter can be constructed with little to no prior experience, in less than 15 minutes, using readily available commercial components, and offers robust operation.

Combined, these metrics facilitate broad adoptability of nanoESI technology for ultrasensitive proteomics where limited volumes or amounts of protein digests need analysis.

Applications:

  • Nano-spray interface device to enhance ionization efficiency
Advantages:

  • Rapid construction (<15 minutes) without dangerous chemical treatments
  • Robust operation
  • Fast analysis time (~30 minutes)
  • Ultrasensitive detection (1 ng protein digest)
  • Low sheath fluid flow rates of 1-50 nL/min