Page 97 - Tandem Techniques

Page 78

It is apparent that a tandem system incorporating some chiral measurement, or even a chiral
spectrometer in conjunction with a suitable separation technique, could be extremely useful in drug
analysis or in the separation and identification of physiologically active materials.

The basic apparatus that is used for measuring circular dichroism is shown in Figure 2.20. It consists of
a light source, a linear polarizer, a Fresnel rhomb that converts the linear polarized light to circularly
polarized light, a sample cell, and finally an appropriate light intensity measuring device.

The rotation of the linear polarizer ± 45°, to the appropriate Fresnel rhomb axis, induces the generation
of left or right polarized light.

Figure 2.20
The Basic Apparatus for Measuring Circular Dichroism.

The modern form of the CD spectrometer is shown in Figure 2.21, which would be the type appropriate
for tandem operation. Light from a broad emission source passes through a chopper and then to a
monochromator that allows light of a selected wavelength to be passed through a filter to the polarizer.
The polarizer can be a Rochon prism and the polarized light would then be passed through a
photoelastic modulator (Pockels cell), the function of which will be described below. The selected left
or right