Refraction of Liquids for Calibration Purposes

Index of Refraction of Liquids for Calibration Purposes Index of Refraction of Air Characteristics of Laser Sources Infrared Laser Frequencies... 

This instrument is used to measure the difference in refractive index or in optical path length between two liquids by a null method. The measurement is converted into a difference in composition by means of a calibration curve. The use of the instrument is restricted to systems with a small difference in refractive index, otherwise a large number of standard mixtures have to be made up for calibration purposes. 

An instrument known as a refractometer has been used for many years to measure the refractive index of liquids and liquid solutions for the purpose of both quantitative and qualitative analysis (see Chapter 15). A refractometer measures the degree of refraction (or bending) of a light beam passing through a thin film of the liquid. This refraction occurs when the speed of light in the sample is different from a reference liquid or air. The refractometer measures the position of the light beam relative to the reference and is calibrated directly in refractive index values. It is rare for any two liquids to have the same refractive index, and thus this instrument has been used successfully for qualitative analyses. 

The purpose of probe calibration in liquid—solid systems is to ascertain if the responding curves of the probe and the measuring system are linear for the test materials. Since in liquid-solid systems particles are distributed uniformly, the reproducibility would be perfect. If the calibration results of the whole system are linear, for gas-solid systems the only parameter which needs to be changed is the index of refraction of the continuous phase. Experiments showed that in the case of a gas-solid system, under the same experimental conditions the output signals of concentration were larger that those for the liquid—solid systems. 

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