Agilent InfinityLab LC Series RID User Manual
19
1
Introduction to the Refractive Index Detector
Detection Principle
Measurements
Initially both sample and reference cell are flushed with mobile phase. The
reference cell is then closed and solvent flows only through the sample cell. The
refractive index of the mobile phase in both cells is the same and the position of
the zero glass can be adjusted so that the detector is in optical balance with an
equal amount of light falls on each diode.
When sample elutes from the column into the sample cell the refractive index of
the cell contents changes. The change in refractive index deflects the light beam
as it passes through the flow cell resulting in an unequal amount of light falling
on each diode. The change in current from the diodes that this causes is
amplified and used to produce the calibrated detector signal. This signal
expressed, as nano Refractive Index Units (nRIU), corresponds to the difference
between the refractive index of sample in the sample cell and the mobile phase in
the reference cell.
Figure 6
Optical Path
Zero glass
Deflected light
Collimator lens
Reference cell
Mirror
Condenser lens
Incident light
Sample cell
Lamp
Diodes