Technology for Polarization Measurement

Circular Dichroism

Circular dichroism is the differential absorption (A = AL – AR) between left and right circularly polarized light in the UV-Visible region. It is a measurement of the optical activity of chiral molecules.

SETUP

T4_2-1-3-1_B

PEM Setting: quarter-wave retardation (λ/4)
Polarization Modulation: right and left circular polarization
Lock-in reference: PEM’s 1st harmonic

POLARIZATION MODULATION

After the PEM, the light beam is modulated between right and left circular polarization at the modulator frequency (1f).

T4_2-1-3-1_A

When the sample absorbs right and left circular polarization differently, the light intensity on the detector will have a 1f AC signal that is related to A. In principle, two separate spectra, AL and AR, can be taken with left and right circularly polarized light and then subtracted to get A. However, A is normally several orders of magnitude smaller than AL or AR. The stability and dynamic range of a common instrument cannot meet such a requirement. Therefore, PEM modulation makes the CD spectrometer practical.

APPLICATIONS

Structural study and chiral analysis in biochemistry; analytical and physical chemistry; drug and pharmaceutical industry

TYPICAL HEAD ASSEMBLIES

I/FS50
II/FS42

ADDITIONAL TOOLS

Circular Dichroism Complete Solution Package

FURTHER READING

T. C. Oakberg, Application note– Linear and Circular Dichroism, Hinds Instruments, Inc. (1991).

A. F. Drake, J. Phys. E: Sci. Instrum. 19, 170 (1986).

Linear & Circular Dichroism Application Note

 
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