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 established either 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 which provides a means of establishing 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.

No Coating (-N-)

>Standard coated tip illustrated

Voltage is applied to the sample directly through liquid-junction contact. Electrical connection is made through a conductive—usually metal—union connecting the emitter to the column.

Standard coated tip illustrated

Electrical contact is made to the metal union holding the emitter. The voltage passes to the mobile phase in the gap between the emitter and the transfer line. PicoTips that are uncoated have -N- in their stock numbers. In one configuration the union holding the emitter is made from a conducting metal. In another configuration the voltage is applied through a wire electrode inside a PEEK MicroTee.

PROS: Most robust method for applying voltage. No conductive coating is necessary to make contact, so there is no coating to wear away. Voltage applied at the liquid junction is more stable and direct. When using a PicoFrit column, this also provides electrical contact pre-column, which ensures stable, reliable spray as well as higher sensitivity. Uncoated emitters are also more economical.

CONS: A conductive union must be used to apply voltage.

Distal Coating (-D-)

Standard coated tip illustrated

Electrical contact is made to the conductive coating near the distal end of the emitter. Voltage travels back the length of the emitter to ake contact with the sample at the junction with the column.

Standard coated tip illustrated

Electrical contact is made to the outside of the emitter, which has a conductive coating on the distal end. The voltage contacts the mobile phase through the gap between the emitter and the transfer tubing. PicoTips with a distal coating have -D- in their stock numbers. The union holding the emitter is made from non-conductive material, such as PEEK.

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

CONS: Because the conductive material is on the back end of the emitter, and not near the tip, the conductive coating wears longer than a standard tip coating. In this setup, the voltage applied to the exterior of the emitter travels back the tip (away from the inlet) and makes contact with the sample at the junction where it is connected to the column, simulating liquid junction connection. This method is more robust than the standard tip coating voltage application.

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.

Standard coated tip illustrated

Electrical contact is made to the outside of the tip. The emitter has a conductive coating that extends to the very tip. 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.

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

CONS: Any coating applied to the emitter will eventually wear out over time. Because the conductive material is used to provide voltage to the sample, at the tip of the emitter, it wears out even more quickly than the distal coating. Additionally, 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. If you must make electrcal contact with the outside of the emitter, distal coating is recommended.

Congratulations - You've selected an emitter!