Liquid Chromatography - The Refractive Index Detector 2

Courtesy of the Waters Chromatography

Figure 24. The Refractive Index Detector

The refractometer shown in figure 24 monitors the deflection of a light beam caused by the refractive index difference between the contents of the sample cell and that of the reference cell. A beam of light (usually from an incandescent lamp) passes through an optical mask that confines the beam to the region of the cell. The lens collimates the light beam which then passes through both the sample and reference cells to a plane mirror. The mirror reflects the beam back through the sample and reference cells to a lens which focuses it onto a photo cell. The location of the beam, rather than its intensity, is determined by the angular deflection of the beam resulting from the refractive index difference between the contents of the two cells. As the beam changes its position of focus on the photoelectric cell, the output changes and the difference signal is electronically modified to provide a signal proportional to the concentration of solute in the sample cell.