New Method for Fabrication of Fused Silica Emitters with Submicrometer Orifices for Nanoelectrospray Mass Spectrometry

In this paper, we describe a new method for fabrication of nanoelectrospray emitters. The needles were pulled from fused silica capillary tubing, which was melted by means of a plasma, formed by electrical discharges between two pointed platinum electrodes. A key feature of the pulling device is a rotating configuration of the electrodes, which results in an even radial heating of the capillary. The construction of the setup is straightforward, and needles with a variety of shapes can be fabricated, including orifices of submicrometer dimensions. Pulled needles with long tapered tips and an orifice of 0.5 μm were utilized for electrospray ionization mass spectrometry (ESI-MS) of discrete sample volumes down to 275 pL. The picoliter-sized samples were transferred into the tip of the needle from a silicon microchip by aspiration. To avoid a rapid evaporation of the sample, all manipulations were performed under a cover of a fluorocarbon liquid. The limit of detection was measured to be ca. 20 attomole for insulin (chain B, oxidized).