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The constant k is an instrument sensitivity constant (calibration constant) for the refractometer.
Because the refractometer is not designed to be an absolute refractometer, but a detector, the
only way to determine the instrument constant is by calibration with a standard solution of
known concentration and dn/dc value. This procedure is available in Viscotek’s TriSEC
software. Once the instrument constant is determined by calibration, it should remain constant
for an indefinite period of time unless the solvent is changed, some optical re-alignment is
made, or the cell is discolored due to residue accumulating on its surface.
Prism
Detector
Detector
Amplifier
R
f
V
OUTPUT
Source
S
R
Cell
Mirror
n
n
S
R
d
L
θ
Figure 8 Optical Schematic of RI detector
A.3.b
Components
The RI detector is fully contained within the RI block assembly, as noted previously. It
consists of the aluminum block and its two endcaps, one covering the source/detector end (not
shown in
Figure 9
), and the other cap covering the cell/mirror end (the front end).