EVAPORATIVE LIGHT SCATTERING

Evaporative Light Scattering Detectors involves nebulization of the column effluent to an aerosol, followed by solvent vaporization to produce a small solute droplets, and then these droplets detected in the light scattering cell. System consists of three parts the nebulizer, the drift tube, and the light scattering cell.

Couresy of Alltech Associates, Inc.

Analytical column outlet is connected directly to the nebulizer . The column effluent is mixed with a stream of nebulizing gas to form an aerosol. The aerosol consists of a uniform dispersion of droplets. The lower the mobile phase flowrate, the less gas and heat are needed to nebulize and evaporate it. Reduction of flowrate by using 2.1mm I.D. column should be considered when sensitivity is important. The gas flowrate will also regulate the size of the droplets in the aerosol. Larger droplets will scatter more light and increase the sensitivity of the analysis. The lower the gas flow used, the larger the droplets will be. It is also important to remember that the larger the droplet, the more difficult it will be to vaporize in the drift tube. Unvaporized mobile phase will increase baseline noise. There will be an optimum gas flowrate for each method which will produce the highest signal-to-noise ratio.

Volatile components of the aerosol are evaporated in the drift tube .

LIGHT SCATTERING CELL

The nebulized column effluent enters the light scattering cell. In the cell, the sample particles scatter the laser light, but the evaporated mobile phase does not. The scattered light is detected by a silicone photodiode located at a 90 angle from the laser. The photodiode produces a signal which is sent to the analog outputs for collection. A light trap is located 180 from the laser to collect any light not scattered by particles in the aerosol stream.