Choosing the Right Emitter

STEP 2: Select an online PicoTip emitter for your flow rate

Online PicoTip Emitters

Fused-silica PicoTip emitters come in three options: The SilicaTip, the TaperTip, and the PicoFrit. The SilicaTip and TaperTip are standard electrospray emitters and differ in size and therefore operational flowrates. TaperTips are very robust emitters and are used in microspray applications. If your application permits a microspray flow rate (0.2 to 3 µL/min), we recommend starting with a TaperTip and familiarizing yourself with the low flow format before switching to a smaller SilicaTip or PicoFrit.

Your emitter mounting hardware must accommodate 150 or 360 µm outside diameter (OD) fused-silica tubing. 360 µm is preferred since it is easier to handle and is available in a wider range of sizes and styles. Standard emitter length is 5 cm for SilicaTips and 50 cm for TaperTips.

SilicaTips
The SilicaTip is the highest performance emitter (U.S. patent 5,788,166) for online low-flowrate ESI-MS. Sizes are available to support flow rates from 500 nL/min to less than 1 nL/min. Determine your target flow rate, locate the corresponding tip size on the table below, and then determine what coating style your equipment supports.

SilicaTip™ Size vs. Flow Rate
Tip Size, ID (µm)Flow Rate* (nL/min)
520-100
850-300
10100-400
15150-400
30300-1000

Above are approximate flow rate ranges over which the tips will generate a stable electrospray plume without sheath gas assistance. Variations in experimental parameters (mobile phase composition, applied voltage, source design etc.) may alter performance considerably.

TaperTips
The TaperTip is a fused-silica emitter with no internal taper (the walls inside the tip are parallel) and are useful at flow rates from 0.2 to 3 µL/min., which are higher than the standard SilicaTip. TaperTips offer superior durability and, due to having no internal taper, provide high resistance to clogging. Determine your target flow rate, locate the corresponding tip size on the table below, and then determine what coating style your equipment supports.

TaperTip™ Size vs. Flow Rate
Tip Size, ID (µm)Flow Rate* (µL/min)
200.2-0.5
500.2-1
750.3-2
1000.4-3

Above are approximate flow rate ranges over which the tips will generate a stable electrospray plume without sheath gas assistance. Variations in experimental parameters (mobile phase composition, applied voltage, source design etc.) may alter performance considerably.

PicoFrits
The PicoFrit is a SilicaTip that has been modified with the placement of a porous frit inside the taper of the tip. The frits are useful as in-line filters, as a source of turbulent flow for solvent mixing, and as a bed for packing chromatographic media. Pre-packed PicoFrit columns (under license of U.S. patent 5,572,023) are available packed with different media that make nanobore LC-MS both easy and affordable. We strongly recommend switching to a PicoFrit if your analytical configuration connects a nanobore column to an emitter. Determine if you want to purchase a pre-packed PicoFrit column or a self-pack PicoFrit column.

Once you've determined the physical dimensions of your emitter based upon your target flow rate, how will you apply voltage to your sample?

NEXT: Select a conductive coating style