Nebulisation

What is nebulisation?

Nebulisation is the process of converting a flowing liquid into a fine spray of droplets.

It is a crucial step in many atmospheric-pressure ionisation sources.

Why is it necessary?

LC delivers analytes dissolved in liquid.

Mass spectrometry ultimately requires gas-phase ions.

Nebulisation helps bridge these states:

Liquid → spray → droplets → smaller droplets → gas-phase ions

Pneumatic nebulisation

A high-velocity gas, commonly nitrogen, assists in breaking the liquid stream into droplets.

The gas is often called the nebuliser gas.

Electrospray

In ESI, high voltage applied to the liquid creates a strong electric field.

The liquid forms a characteristic Taylor cone, from which charged droplets are emitted.

Solvent subsequently evaporates.

As droplets become smaller, charge density increases. Eventually the droplets undergo processes leading to progressively smaller charged species and ultimately gas-phase ions.

Factors affecting nebulisation

Important factors include:

• liquid flow rate

• nebuliser gas pressure/flow

• solvent composition

• surface tension

• viscosity

• emitter geometry

• applied voltage

• source geometry

Poor nebulisation

Poor spray formation can produce:

• unstable signal

• reduced sensitivity

• increased noise

• large droplets

• source contamination

• poor reproducibility

A visibly or electronically unstable spray often appears in the data as a fluctuating total ion current.

Key takeaway

Nebulisation converts the incoming liquid into small droplets, enabling efficient solvent removal and subsequent ion formation.