Design, development, and performance of a fiber optics refractometer: Application to HPLC

A fiber optics refractometer has been developed based on a simple low-volume cell (5–7 μl) which confines the liquid to be measured around a waveguide whose multiple reflections can enhance the contrast at the critical angle. The electromechanical and electrooptical design allows the fiber optics refractometer to measure absolute refractive index with manual or automatic readout, and differential operation with automatic tracking that permits its use as a universal detector for gradient elution chromatography. Present sensitivity is approximately 1×10−5 refractive index units in the static mode and 7×10−5 refractive index units in the scanning beam mode. These sensitivities can probably be improved by a factor of 5 by appropriate system changes.