Liquid Chromatography Detectors - LC Detectors Based on Refractive Index Measurement > The Christiansen Effect Detector > Page 27

Figure 16. The Christiansen Effect Detector

In the optical unit there is a pre focused lamp having an adjustable voltage supply to allow low energy operation when the maximum sensitivity is not required. The condensing lens, aperture, achromat and beam splitting prisms are mounted in a single tube which permitted easy optical alignment prevented contamination from dust. The device contains two identical and interchangeable cells. The disadvantage of this detector is that the cells must be changed each time a different mobile phase is chosen in order to match the refractive index of the packing to that of the new mobile phase. The refractive indices of the cell packing can be closely matched to that of the mobile phase by using appropriate solvent mixtures. In most cases solvent mixing can be achieved without affecting the chromatographic resolution significantly (e.g. by replacing a small amount of n-heptane in a mixture with either n-hexane or n-octane depending on whether the refractive index needs to be increased or decreased. However a considerable knowledge of the effect of different solvents on solute retention is necessary to accomplish this procedure successfully. As a result of limitations inherent in his type of detector combined with the general disadvantages of the RI detector per se has not made the Christiansen Effect Detector very popular.