PerkinElmer 200 UV/VIS Series User Manual page 161

Theory of Operation Principles of Operation
Figure 8-2. Diagram of the detector optics.
The diameter of the flowcell entrance aperture determines the bandwidth of the instrument.
While Beers Law holds strictly true only in the case of monochromatic light, it is also desir-
able to maximize the amount of light energy going through the cell for the best possible sig-
nal-to-noise ratios (see "Detector Response Time" in the Application Notes section). In order
to insure high energy throughput while maintaining a narrow bandwidth, the Series 200
UV/VIS LC Detector uses a bandwidth of 5 nm.
In the PerkinElmer dual-beam design, the intensities of the light passing through the sam-
ple flowcell and the reference cell are monitored. After being converted by the photodiodes to
an electric current, the Series 200 UV/VIS LC Detector uses the ratio of the sample light
energy to the reference light energy in order to cancel out fluctuations in lamp output which
affect both light beams equally. Therefore, baselines remain steady and quiet. Only differ-
ences which occur in one path (e.g., in the sample path due to absorption by a compound of
interest) will be amplified and output for analysis.
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