Refractometers, Schmidt, Hand Held Brix, Atago, Fisher

A refractometer measures the extent to which light is bent (i.e. refracted) when it moves from air into a sample and is typically used to determine the index of refraction (aka refractive index or n) of a liquid sample. The refractive index is a unitless number, between 1.3000 and 1.7000 for most compounds, and is normally determined to five digit precision. Since the index of refraction depends on both the temperature of the sample and the wavelength of light used these are both indicated when reporting the refractive index:

A refractometer is a measuring instrument for the speed of light. The result will not be indicated directly but related to the speed of light in air. This comparison is called refractive index. The indication, that a certain material has a refractive index of 1.5 thus means, that the speed of light travels 50% faster through air than through this material.

The refractive index is a value specific to a material. It depends on temperature and wavelength (λ = colour) of the light. Thus using a refractometer, will enable you to determine the concentration of a material, if temperature and wavelength are known. But it is also possible, that different materials have the same refractive index at various concentrations. Thus a clear determination of liquid substances may only be succesful with binary mixtures (Mixtures consisting ot two compounds).

In practice, the refractive index determines the mixing ratio also of multicompound solutions quite exactly and easily as in general only the concentration of one of the componends needs to be determined. Thus it is a quantitative measurement. With known compounds, also quality may be determined. For mixtures like for example olive oil or orange juice, the measuring value within a certain range corresponds to a certain quality. Thus refractometry is a quality control of substances There is a definite correlation between the refractive index and the composition of many two-compound solutions. The best known example for such a mixture is a solution of sucrose in water, which has been studied throughly. A refractometer can be grated in a way that the value may be indicated directly as dry substance %RTS. For sucrose, this unit is also named Brix (abb. Bx). The determination of the density of samples can also be done with refractometry. As a rule in optical measuments density and dry substance corresponds to each other.