Waters 2414, Overview And Maintenance Manual

Page: 15 / 130

June 11, 2015, 715004754 Rev. A
Page 15
1
2414 RI Detector Optics
Principles
This chapter summarizes the Waters
®
2414 Refractive Index Detector features
and describes the theory and principles of operation.
1.1 Use of refractive index detectors
RI detectors are typically used to analyze carbohydrates and lipids and in polymer
analyses by gel-permeation or size-exclusion chromatography. Inherently less
sensitive than other types of detectors, and unsuitable for gradient analyses, their
advantage lies in the universal nature of their response. They are well-suited to
analyzing compounds that lack strong UV chromophores, fluorophores, or
electrochemical or ionic activity.
RI detectors measure changes in the bulk properties of the solvent and the solutes
under investigation, exploiting the improbability that solvents and solutes would share
an identical refractive index.
1.2 Operating principles
1.2.1 Optical refraction
When a beam of light passes from one medium into another, it changes its speed. If
the light enters the second medium at an angle that is not perpendicular to the
medium’s surface, the light is bent (refracted).
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 .
1.2.1.1 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.