How to choose the right emitter ID for your workflow

Small, medium or large emitter ID? Depends on your goals.

Selecting the correct internal diameter (ID) for a constant bore nanospray emitter is one of the most important and often overlooked decisions in LC-MS method development. The emitter ID directly affects spray efficiency, sensitivity, robustness, and susceptibility to clogging. 

Selecting the right ID can be the difference between stable, high-sensitivity data and constant clogging, signal loss, and downtime.

Here we explain how emitter ID influences nanospray performance and provide practical recommendations for selecting the optimal ID for your nano-LC-ESI-MS application.

In a hurry? Skip to TL;DR.

Why internal diameter (ID) matters in nanospray ESI

In nanospray electrospray ionization (ESI), flow rates are extremely low, typically ranging from a few nanoliters to a few hundred nanoliters per minute. At these scales, small changes in emitter ID have effects on:

• Backpressure

• Ionization efficiency

• Particle tolerance

• Long-term robustness 

Small IDs: Maximum sensitivity, minimum tolerance

Typical range: ~5-10 µm ID

Very small internal diameters are often chosen to maximize ionization efficiency. Narrow IDs produce:

• Improved desolvation due to formation of smaller initial droplets
• High sensitivity for low-abundance analytes

Trade-offs:

• Typically requires stricter sample cleanup and filtration

• Higher sensitivity to particulates, salts, and aggregates

• Greater risk of clogging, although constant bore technology reduces this risk compared to pulled emitters.

Best suited for:

• Clean, well-desalted samples
• Trap-and-elute nanoLC setups
• Experienced users prioritizing sensitivity over robustness

Medium IDs: Balanced performance and robustness (Trajan CB Emitter range)

Typical range: ~10-20 µm ID

For many LC-MS workflows, this ID range offers the best compromise between performance and reliability. Medium ID constant bore emitters maintain relatively high ionization efficiency compared to larger IDs while reducing clogging compared to smaller IDs or pulled emitters.

Advantages include:

• Stable nanospray at common flow rates (50-300 nL/min)

• Moderate backpressure

• Improved tolerance to trace particulates

• Typically associated with longer emitter lifetime in routine use

Larger IDs: Maximum robustness

Typical range: ~30 µm ID and above

Larger internal diameters are often selected when robustness is the primary concern.

Advantages include:

• Lower backpressure

• Higher tolerance to particulates and complex sample matrices
• Reduced risk of emitter blockage

• Reduced ionization efficiency due to larger droplets and less efficient desolvation.

Best suited for:

• Complex or minimally processed samples
• Users prioritizing reliability over maximum sensitivity

Sample cleanliness still matters

Even with constant bore emitters to reduce clogging, sample cleanliness still matters.

Consider:

• Inline filters or trap columns

• Sample centrifugation or filtration

• Desalting and cleanup steps

• Avoiding dried-down samples with precipitates

Choosing a slightly larger ID is often the simplest and most effective safeguard against real-world sample variability.

Final thoughts: Choose for the weakest link

The “best” emitter ID is not the smallest one - it’s the one that matches the weakest link in your workflow. If your samples are pristine and sensitivity is paramount, small IDs may be ideal. If your samples vary or runs must be unattended, a modestly larger constant bore ID will usually deliver better overall performance.

By thoughtfully selecting the internal diameter of your constant bore nanospray emitter, you can achieve a stable, sensitive, and robust nanospray that supports both high-quality data and efficient lab operation.

TL;DR

As a quick rule of thumb, refer to the following to choose your ESI emitter ID:

• Maximum sensitivity → 5–10 µm ID

• Balanced performance → 10–20 µm ID

• Maximum robustness → 30 µm ID and above

Make the right choice

Explore Trajan CB Emitter options using our emitter selection guide >