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The relationship between the refractive indices of the two media and the
angles of incidence and refraction is described by Snell's law:
n
(sin θ
) = n
1
2
1
where
= Angle of incidence
θ
1
θ
= Angle of refraction
2
n
= RI of medium 1
1
n
= RI of medium 2
2
You can use Snell's law to calculate the RI of a sample solution from the angle
of incidence, the RI of the solvent, and the angle of refraction.
Using changes in RI for sample detection
As the separated components of a sample pass through the refractometer flow
cell, these events occur:
•
The composition of the sample solution in the flow cell changes.
•
The RI of the solution changes.
•
The light beam passing through the solution is refracted.
The refractometer detects the position of the refracted light beam, creating a
signal that differs from the baseline signal.
The following figure shows how refraction by the sample in the flow cell
changes the proportion of light on each element of the photodiode.
(sin θ
)
2
October 13, 2014, 715003547 Rev. C
Operating principles
19
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