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-1 Optical System
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1 Optical System
The deflection type refractive index detector, the
Shodex
RI-501EX, has a
newly developed three-chamber type flow cell, consisting of a single sample
cell chamber and two reference cell chambers as shown in Fig. 4.1.
An eluent that contains a sample flows in the sample cell chamber like the
conventional flow cell and the two reference cell chambers are filled with an
eluent that does not contain the sample. Under such conditions, the light
beam passes the flow cell in a way to penetrate the three cell chambers as
shown in Fig. 4.1. When the sample cell chamber is filled with an eluent that
does not contain the sample, the light beam is straight.
However, when an eluent containing the sample flows in the sample cell
chamber, the light beam is refracted. This deflection scale of the light beam
can be taken as the displacement of the light spot formed on the photo
sensor. Since the three-chamber type flow cell has two refracting interfaces,
the light beam is refracted twice according to the difference of the refractive
index. For this reason, the RI-501EX provides twice the sensitivity of
conventional flow cell having a single interface.
1: Light beam
2: Sample cell
3: Reference cell
4: Light beam at the
5: Light beam at the
6: Displacement
7: Photo sensor
n
s
: Refractive index of liquid
in sample cell
n
r
: Refractive index of liquid
in reference cell
Fig. 4.1 Principle of detection of the deflection type
A variety of ingenious devices are provided in the optical system to enhance its
operational stability and make the detector more compact. The light beam from
the light source passes the flow cell through condenser lens, slit No.1,
collimator lens and slit No.2. The light is reflected by the mirror which exists just
behind the flow cell and it forms an image of slit No.1 onto the photo sensor
through the flow cell, slit No.2, collimator lens and null glass.
The photo sensor has two light receivers placed side by side.
:
Light source
4 :
Collimator lens
7 :
Mirror
2 :
Condenser lens
5 :
Slit No.2
8 :
Null glass
3 :
Slit No.1
6 :
Flow cell
9 :
Photo sensor
Fig. 4.2 Optical System
4. Detection Principle
4. Detection Principle
4. Detection Principle
4. Detection Principle
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s
n
r
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n
r
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