Liquid Chromatography Detectors - LC Detectors Based on Refractive Index Measurement > The Interferometer Detector > Page 31
The circularly polarized beams will, therefore, interfere to yield a linearly polarized beam which is rotated radians, and the amplitude of the light striking the photocell (Ap) will be given by
An extremely high sensitivity is claimed for this system but it is difficult to interpret the data in terms of minimum detectable concentration The smallest cell (1.4 ml) is reported to give a sensitivity of about 2 x 10-7 RI units at a signal-to-noise ratio of two. Consequently, for benzene (RI = 1.501) sensed as a solute in n-heptane (RI=1.388 ) this sensitivity would represent a minimum detectable concentration of 5.6 x 10-5 g/ml. The alternative 7 ml cell would decrease the minimum detectable concentration to about 1 x 10-6 g/ml, similar to that obtained for other refractive index detectors.
A number of LC detectors have been developed that are either based on refractive index measurement or function on some physical property of the mobile phase system that is related to the refractive index. Although most are not commercially available, they demonstrate the range of sensing techniques that have been investigated as possible methods of detection.