Choosing the Right Emitter

STEP 3: Select the right conductive coating style

In order to perform electrospray a means of electrical contact must be supplied. Contact is either established through a conductive coating applied to the emitter or directly to the mobile phase through a junction contact. Each style of emitter is available with a multi-layer conductive coating (U.S. pat. 5,788,166) to establish contact with the spray solvent at the end of the tip. Emitters are also available uncoated for junction contact inside a metal union. Some styles of emitters are also available with our distal coating that provides a means to establish in-union electrical contact without having to resort to stainless steel fittings. The distal coating was specifically designed to work with our expanding line of nanospray adapters.

Proximal or Standard Coating (-CE-)

Standard coated tip illustrated

Electrical contact is made to the conductive coating near the tip of the emitter. Voltage travels towards the tip and makes contact with the sample as it exits the emitter.

The electrical contact is made to the outside of the tip. The emitter has a conductive coating that extends to the tip where the voltage contacts the mobile phase as it exits the emitter. PicoTips with a standard coating have -CE- in their stock numbers. The union holding the emitter is made from non-conducting material, such as PEEK, but can be metal. Often, a separate wire with a clip is applied to the conductive coating.

PROS: The physical method of making electrical contact is simple. Most older mass specs enabled electrical contact in this fashion.

CONS: Having the conductive material this close to the inlet, where electrical potential is highest, makes this the tip much more prone to arcing and coronoa discharge, both of which ruin the emitter.

No Coating (-N-)

Standard coated tip illustrated

Voltage is applied to the sample directly by means of inserting a platinum wire connected to the high voltage of the mass spectrometer.

The electrical contact is made to the mobile phase via the insertion of a platinum wire into the inlet end of the emitter. This wire is connected to high-voltage.

PROS: No conductive coating is necessary to to make contact, so there is no coating to wear away

CONS: Insertion of the wire into the emitter takes steady hand; not all of the sample may be used.

Congratulations - You've selected an offline emitter!