Optical rotation dispersion and circular dichroism

 

Optical rotation dispersion

·     Linear polarized light is a combination of a left- and right-circular polarized wave

·     One of these waves is retarded more than the other

·     This resulted in a twist of the optical axis

 

[a]_l = a_(l) / c . d

 + = right             - = left

 

Typical Dn about 1-2 . 10^-6 = e.g. a 0.1 mmolar solution of an amino acid (1 cm path) will rotate the light about 1 degree.

 

Circular dichroism

 

·     Linear polarized light is a combination of a left- and right-circular polarized wave

·     Not only one of these waves is retarded more than the other but moreover one is absorbed with an increased or decreased absorption coefficient

·     To quantify the CD the difference of e_r minus e_l (versus frequency) is recorded.

 

 X_(l) = ln10 . 90 . p . (e_l - e_r) . c . d

 

What is circular polarized light ?

A constant field vector is rotating in a spiral.

In which way is circular polarized light obtained?

Linear polarized light is rotated via a l/4 – plate =

The beam is split into 2 beams (by a special material) and after passing through the plate both beams interfere with a well defined phase angle.