Liquid Chromatography Detectors - The Evaporative Light Scattering Detector > Page 73

The Evaporative Light Scattering Detector

The evaporative light scattering detector, as its name implies, utilizes   a spray that continuously atomizes the column eluent into small droplets. These droplets are allowed to evaporate, leaving the solutes as fine particulate matter suspended in the atomizing gas.



Courtesy of Polymer Laboratories Inc.


Figure 48. A Diagram of the Evaporative Light Scattering Detector

The atomizing gas can be air or, if necessary, an inert gas. The suspended particles pass through a light beam and the scattered light viewed at 45o to the incident light beam by means of a pair of optical fibers. The scattered light transmitted through the fibers is sensed by a photomultiplier and the output electronically processed and passed either to a computer data acquisition system or to a potentiometric recorder. A diagram of the light scattering detector is shown in figure 48. Theoretically, the detector responds to all solutes that are not volatile and as the light dispersion is largely Raleigh scattering, the response should be proportional to the mass of solute present; as a consequence, it is sometimes referred to as the mass detector. For a linear response, the droplet size must be carefully controlled as it also determines the particle size of the dried solutes.