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1 The ACQUITY Refractive Index Detector
The extent to which a medium refracts light is its refractive index (RI),
calculated as the ratio of the velocity of light in a vacuum to the velocity of
light in the medium. It is a physical property of the medium, with a
dimensionless integer value represented by the letter n.
Factors that affect RI
The refractive index of a medium depends solely on the speed of light through
the medium, which is constant for a given wavelength of light at a specified
temperature and pressure.
Wavelength
The refractive index of a medium has a specific value that changes with the
wavelength of the incident light beam. The detector uses monochromatic light
at a fixed wavelength, so the effect of different wavelengths of light on RI is
not discussed in this guide.
Density
The density of the medium also affects its RI. At a fixed wavelength, the
relationship between the density of a medium and its RI is generally, but not
necessarily, linear. These are the most important of the factors that affect the
density of a medium are:
•
Composition
•
Temperature
•
Pressure
The following figure illustrates the effect of density on the RI of two solutions.
The refractive index of a sucrose solution changes linearly with concentration
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October 13, 2014, 715003547 Rev. C
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