Is an instrumental analytical method using rotation of polarized light by some substances as measure of their concentration in a solution.

The instrument used is called polarimeter

Un-polarized light from the light source is first polarized.

This polarized light passes through a sample cell.

If an optical active substance is in a sample tube , the plane of the polarized light is rotated .

The rotation is noticed by looking through the analyzer as a change in the intensity of illumination.

To reach the same illumination as was without an optical active sample the analyzer must be turned around for an angle.

Reading is taken in degree angle (α ) .

Light source

Un-polarized light

Polarized light

polarizer

Sample tube

Rotated polarized light

analyzer

Degree of rotation measured

viewer

Compounds containing Asymmetric carbon atoms rotate the plane of polarized light.

The phenomena is called optical rotation and such substances are optically active compounds.

By measuring the angle of rotation the concentration of a substance in solution is determined.

Carbon atom that attached to four different groups called Asymmetric

4 groups of atoms attached to the carbon atom can be arranged in 2 different way that are mirror images to each other.

Molecules that cannot be superimposed on their own mirror image are said to be chiral

Two mirror images of a chiral molecule are called enantiomers or optical isomers. Pairs of enantiomers are often designated as “right-

-" and "left-handed."

Enantiomers can rotate plane of the polarization of plane polarized light into :

Dextrorotatory(+) enantiomers giving a positive optical rotation.

Levorotatory (-) enantiomers giving a negative optical rotation.

In stereochemistry, the specific rotation of a chemical compound is defined as the observed angle of optical rotation α when plane-polarized light is passed through a sample with a path length of 1 decimeter and a sample

concentration of 1gm/1ml.

•Sucrose +66.47°•Lactose +52.3°•Cholesterol  −31.5°•Camphor  +44.26°•Penicillin V +223°•taxol −49°•(S)-bromobutane +23.1°•(R)-bromobutane −23.1°•(+)-cavicularin +168.2°

Nature of the sample is described by introducing the specific optical rotatory power of substance , defined as:

where:

[α]λT is the specific rotation.

T is the temperature.λ is the wavelength of light.α is the angle of rotation.l is the length of the polarimeter tube in decemeter.c is the concentration of solution in gm /100ml.

]α[λT = 100 α/ l c

] α[λT = α / l ρ

]α[λT = α / l

This equation, For pure liquids. l = The path length in decimeters.

ρ = The density of the liquid in g/mL.T = Temperature (given in degrees Celsius) Λ = Wavelength (in nanometers) 589 nanometer (the sodium D line).

This equation, For Solutions. l = Path length in decimeters .

C= Concentration in g/mL.T = Temperature (given in degrees Celsius) Λ =Wavelength (in nanometers) 589 nanometer (the sodium D line).

used to identify which isomer is present in a sample (dextro or levo) .

It can also be used to measure optical activity of racemic mixture (indicating an equal (1:1) mixture of dextro and levo isomers).

Concentration and purity measurements are especially important to determine product or quality in the food & beverage and pharmaceutical industries

The type of nature of sample (e.g: sugar solution).

Concentration of the optical active components.

The length of the sample tube.

The wavelength of the light source.

Temperature of the sample.

The type of nature of sample (e.g: sugar solution).

Concentration of the optical active components.

The length of the sample tube.

The wavelength of the light source.

Temperature of the sample.

What do the measured

angle depend on?

In side a human body each isomer act differently In some cases one of the isomers exhibit toxic effect ,in other cases each isomer show different kinetic.

Recently FDA guideline have effectively determined that mixtures of chiral compounds can no longer be brought to the pharmaceuticals

market place.