Differential Refractometry - Waters 2410 Operator's Manual

By keeping wavelength, temperature, and pressure constant, the changes in RI measured
by the refractometer are due only to changing sample concentration. A solution with a high
concentration of a solute refracts a beam of light more than a dilute solution. Therefore,
1
high concentrations of sample yield large peaks.

1.2.2 Differential Refractometry

The 2410 differential refractometer can measure extremely small changes in refractive
index to detect the presence of sample. The small difference in RI between a reference
solution and a sample solution is referred to as ∆n. ∆n is expressed in refractive index
units (RIU).
The 2410 differential refractometer measures ∆n values as small as 5 × 10
detecting the difference in the amount of light falling upon each of the elements of the
dual-element photodiode (see
External Angle of Deflection
The amount of light falling upon the elements of the photodiode is determined by the
external angle of deflection ( φ ), as shown in
of the shift (∆x) of the image cast on the photodiode by the light beam.
illustrates the external angle of deflection ( φ ) and its dependence on the
Figure 1-5
difference in RIs between the reference and sample sides of the flow cell.
22 Waters 2410 Theory of Operation
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Figure 1-4).
1-5. The φ determines the magnitude
Figure
–8
RIU by