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
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).
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
PEMs
INSTRUMENTATION
FURTHER READING
Linear & Circular Dichroism Application Note, T.C. Oakberg, Hinds Instruments, Inc. (1991)
Contact us to see how Hinds Instruments works with our customers to solve complex metrology problems.