| 摘要 |
<p>An ultra-low flow rate electrospray ionization (ESI) source provides flow rates in the range of 1.0 nL/min or less. The source is comprised of a needle (12) which is fabricated by laser-heated pulling of fused-silica tubing, followed by chemical etching and surface metallization. The pulling results in formation of a slowly tapering capillary (40) within the needle (12) which tapers to a tip (22) having a very small inner diameter. The etching process sharpens the outer wall (42) of the needle (12) to a very sharp tip, and the combination of these parameters results in the ultra-low flow rate capability. After a metal electrical contact (44) is formed on the exterior wall of the needle (12), an electrically insulating overcoating (46) is preferably deposited thereon which locks the contact (44) in place, thereby greatly increasing needle life, and also restricting the electrical contact point to the very tip of the needle (12). Although the use of the ultra-low flow rate ESI sources increases sensitivity to sampling errors, a mechanism is also provided to minimize one primary source of such errors, evaporation induced hydrodynamic flow, in capillary electrophoresis (CE). An injection system (60) is provided which enables a retractable droplet of buffer solvent to be positioned in contact with the tip end of the ESI needle during sample loading. This prevents evaporation from the tip end, thereby eliminating hydrodynamic flow into the distal end (63) of the capillary column (62) used in the CE process.</p> |
