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Technology Description	A procedure for fabricating fused silica emitters for electrospray ionization-mass spectrometry (ESI-MS) in which the end of a bare fused silica capillary is immersed into aqueous hydrofluoric acid, and water is pumped through the capillary to prevent etching of the interior.
Category	Technology
PRC	Pacific Northwest National Laboratory
PubMed ID	17105173
Author	Ryan T. Kelly, Jason S. Page, Quanzhou Luo, Ronald J. Moore, Daniel J. Orton, Keqi Tang, and Richard D. Smith
Publication Description	The authors described their process for fabricating high aspect ratio silica ESI emitters based on chemical etching has enabled nanospray emitters to be produced that have no internal taper and are resistant to clogging. The authors show that the use of 5-ím i.d. emitters at flow rates as low as 5 nL/min provided a stable nanospray in aqueous solvents which is often problematic for ESI. The absence of mechanical processing and the effective etch-stop mechanism in this fabrication technique enabled a high degree of reproducibility between different emitters.
Methodology	A short piece of capillary tube is immersed in hydrofluoric acid (HFA) while water is pumped through it. Surface tension pulls the HFA up the outer sides, thereby etching the the surface to a taper. Removing the tube halts etching and yields an ESI emitter.