A Spectroscopic Refractometer for Temperature-Independent Refractive Index Detection

This paper presents the working principles of spectroscopic refractive index detection. The method is based on measurement of the differences in the wavelength dispersion of the refractive index of a solute and a solvent. The basic theory of the method is outlined, and it is shown that spectroscopic refractive index detection has the potential to eliminate the thermal noise that is connected with conventional refractive index detection. The design and testing of a spectroscopic refractometer are described. The device is based on light deflection in a liquid prism and utilizes a deuterium lamp and a CCD detector in order to measure the deflection at several wavelengths simultaneously. When thermal variations of 4−5 °C are evoked, the noise observed corresponds to 4 × 10-3 °C, while the gain obtained in the signal-to-noise ratio is a factor 40. It is also shown that the sensitivity and selectivity of the method can be controlled by spectrochemical modification of the refractive index spectrum of the solvent...