Realizing nano electrospray ionization using disposable pipette tips under super atmospheric pressure.

Nano electrospray with a solution flow rate below 100 nL min(-1) is usually performed using a metallized pulled glass capillary with an inner diameter tip of <10 μm. In this paper, we demonstrated that it was possible to achieve a stable solution flow rate of ~10 nL min(-1) for an aqueous solution using a disposable plastic pipette tip with an inner diameter of 100 μm as an ESI emitter. This pipette tip (gel loading tip) was originally designed for the loading of sample onto the gel in gel electrophoresis. The inner and outer diameters were much larger than those of a nanoESI emitter, but the low solution flow rate could be sustained by conducting the electrospray under a super-atmospheric gas pressure. The high pressure condition ensured the absence of electrical discharge which was essential for stable electrospray of aqueous solution. ESI with this low cost tip was equally as sensitive as the standard nanoESI emitter and capable of producing a long lasting signal from a small amount of sample liquid. Due to a small initial droplet size under the low flow rate regime, ESI with the present method exhibited the property of nanoESI where the ion suppression of the hydrophilic analyte by the hydrophobic compound present in the solution was greatly reduced. Furthermore, owing to its larger inner diameter, the tip relatively easily avoided the clogging problem often encountered when dealing with "dirty" samples when compared with a nanoESI emitter made from a fine glass capillary.