Differential Refractometer:

It monitors the difference in refractive index between the references (mobile phase) and the column eluent. It responds to any solute whereas refractive index is considerably different from that of the mobile phase. A schematic description of a differential refractive index detector is display in Figure where solvent passes by one half of the cell and then it passes through another chamber where eluent flows.

Figure: A schematic illustration of a differential refractive index detector

Two compartments are separated by a glass plate mounted at an angle such that bending of the incident beam occurs if the two solutions differ in refractive index. The resulting displacement in beam with respect to the photosensitive surface of a detector causes variation in the output signal.