MODULATORS :: APPLICATIONS :: Circular Dichroism (CD)

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

 SETUP

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

POLARIZATION MODULATION

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



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, A_L and A_R, 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 A_L or A_R. 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

RESOURCES

Linear and Circular Dichroism Application Note

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).