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Principles of evaporative light scattering detection 1-3
that dry solute particles, consisting only of analytes, reach the light source for
scattering.
Low temperature nebulization
In the detector’s nebulization region, the chromatographic effluent is
transformed into a fine aerosol. A concentric tube, or flow-type nebulizer,
mixes chromatographic effluent with a carrier gas (usually nitrogen)
developing a series of droplets that forms the aerosol that enters a
narrow-orifice drift tube.
Nebulization region and drift tube (representative)
The concentric flow nebulizer allows you to control the carrier gas flow versus
the chromatographic effluent flow rate. High gas flow produces small droplets,
requiring less heat to evaporate the solvent. Conversely, low gas flow produces
large droplets, requiring more heat to evaporate the solvent.
Desolvation
In the desolvation region, the mobile phase evaporates, leaving dried solute
particles in the drift tube.
As the aerosol drops exiting the nebulizer pass through the drift tube, they
become smaller. The carrier gas sweeps the dried, aerosolized solute particles
along to the instrument’s detection region.
Evaporation occurs as a function of time, temperature, and pressure of the
carrier gas. It is therefore important to use HPLC mobile phases that easily
and quickly evaporate and desolvate. Solvents of fairly low boiling point and
low viscosity are best. They include the more commonly used HPLC mobile
phases: water, acetonitrile, methanol, ethanol, and THF. Viscous and
high-boiling solvents might fail to fully separate from the analyte molecules or
Nebulization region Drift tube