Biotage
®
ELSD-A120 User Manual 7
Introduction to the Detector
1
Detector Overview
Detector Overview
Basic Principles of Operation
Nebulization
The eluent inlet is connected to the nebulizer via a short length of
stainless steel capillary tube. The incoming eluent stream passes
through the heated nebulizer and is mixed with the incoming
nebulizer gas stream. The mixed gas and eluent stream form an
aerosol plume containing a uniform dispersion of droplets that then
passes as a continuous flow into the evaporator section. Any larger
droplets or the inefficiently nebulized droplets collect in the nebulizer
chamber waste trap and then drain off via the waste outlet into the
waste container.
Evaporation
After nebulization, the atomized spray is propelled through the
evaporation tube assisted by the carrier gas. In the evaporator
section, the solvent is removed leaving a stream of dry particles of the
analyte. A diffuser located in the evaporator assists in the drying of
the particles, acting as an efficient heat exchanger, prevents ballistic
particles reaching the scattering chamber and randomizes the particle
plume.
Detection
Light in the optical chamber is passed through the detector at right
angles to the direction of particle flow. A light trap is located opposite
the source of light to capture the transmitted incident beam
eliminating internal reflections within the detector body. When pure
solvent is being evaporated, only its vapor passes through the light
path and the amount of light scattered to the photomultiplier is small
and gives a constant baseline response. When a non-volatile solute is
present, a particle cloud passes through the light path, causing light
to be scattered. This scattered light enters the optical aperture of the
detection system and generates a signal response from the
photodiode in real time. The quantity of light detected is dependent
on the solute concentration and solute particle size distribution.
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