42 Agilent 8453 UV-visible Spectroscopy System Operator’s Manual
3 Good Measurement Practices
General Considerations
Optical Specifications of Cells
The accuracy of the readings of a diode-array spectrophotometer is very
sensitive to spatial shifts of the measurement light beam. Cells having non
parallel opposite faces, or so called wedge shaped cells, lead to a spatial shift
of the light beam (see Figure 4). Therefore, the opposite cell walls illuminated
by the analysis light beam have to very parallel. The parallelism is measured in
terms of the angle between the two opposite cell walls. We recommend to use
10 mm path length cells with an angle which is below 0.1 degrees of an arc.
Figure 4 Shift of the Spectrophotometer Light Beam due to non Parallel Cell Walls
Light Beam in
Light Beam out
Light Beam in
Parallel
Cell Walls
Non-parallel
Cell Walls
Light Beam out
Light Beam In
Light Beam In
Light Beam Out
Light Beam Out
Non-parallel
Cell Walls
Parallel
Cell Walls
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