Polarimetry

It is an analytical method used for measuring the polarization and optical activity of various molecules.

1. PHARMACEUTICAL ANALYSIS POLARIMETRY Dr. HARI SINGH GOUR UNIVERSITY, SAGAR, M.P . Presented by- Anjali Sharma

2. POLARIMETRY MODERN POLARIMETER CLASSICAL POLARIMETER

3. POLARIMETRY It is the study of the rotation of polarised light by transparent optically active substance. Polarimetry is based upon the existence of optical activity in a substance. This is a type of qualitative and quantitative analytical technique. Polarimeter is a scientific instrument which measures change in rotation of plane polarised light. Optical activity is unique character for a molecule.

4. OPTICAL ACTIVITY I t is the ability of a chiral molecule to rotate the plane of plane polarised light. As per pasteur absence of symmetry is the necessary criterion for optical activity . The two arrangements that have asymmetric molecule cannot be superimposed. A chiral molecule is non superimposable on its mirror image & have carbon atom attached to four different group also known as chiral center.

5. CONFIGURATION : The representation which shows the sapatial arrangement of the groups of atoms constituting a stereoisomers is known as its confiugration . EPIMERS are the optical isomers that differ only in the configuration around one asymmetric carbon atom (having more than one asymmetric carbon).

6. Enantiomers are chiral molecules that are mirror images of one another & are non- superimposable in nature. Diastereomers are stereoisomers that are not mirror images of one another & are non- superimposable in nature.

7. PLANE POLARISED LIGHT Plane polarised light oscillates only in a single plane when normal light oscillating in all direction passes through a polarizer such as nicol prism. Normal light consists of electromagnetic waves that oscillates in all direction. Circularly polarised light represents a wave represents a wave in which the electrical component spirals around direction of propagation of the ray,either clockwise or anticlockwise.

8. Electric field of plane polarised light is composed of two components. Right circularly polarised (RCP) Left circularly polarised (LCP) The plane beam is vector sum of these two component . The extent of retarding the plane polarised light through a medium is known as refractive index of that medium.

9. When the medium is optically inactive both the component s are retarded to the same extent. when the medium is optically active the component is retarded to different extent due to difference in refractive indices of the medium for LCP & RCP. This phenomenon of the difference in the velocity of LCP& RCP light is called circular birefringence. Due to circular birefringence plane of polarization inclined at an angle. Polarization involves the separation of natural light into its mutually perpendicular components.

10. The angle of incidence selected is such that the criticle angle of reflection is exceeded for one ray but not for the other. But the beam emerging out is not parallel to the incident beam and this can be overcomed by cementing the seconed prism. It also reduces the loss of intensity . Linearly polarised light is passed through the optically active solution & the plane polarised light rotated by an angle .

11. SPECIFIC ROTATION Change in the orientation of monochromatic plane –polarized light , per unit distance –concentration product , as the light passes through a sample of a compound in solution. It is a property of a chiral chemical compound. It is an intensive property. Used in quantitative analysis of optically active solute using polarimetry .

12. POLARIMETER Principle : Polarimeter measures the rotation of polarised lights as it passes through an optically active fluid. The measured rotation can be used to calculate the value of solution concentrations. Construction : A polarimeter consists of a polarized light source,an analyzer,a graduated circle to measure the rotation angle and sample tube. Working : The polarized light passes through the sample tube and exhibits angular rotation to the left (-) or right (+). On the side opposite the polarizer is the analyzer. Visual fields are manually adjusted by the users to measure the optical rotation angle by using optics .

13. TYPES OF POLARIMETER Laurent’s half-shade polarimeter Biquartz polarimeter Lippich polarimeter X-ray polarimeter Quartz-wedge polarimeter

14. APPLICATIONS Quantitative application- For determining the specific rotation if concentration is known. For determining the concentration if specific rotation is known. Differentiating optical substances from optically inactive species. Qualitative application- ORD & CD measurements can be used for studying configuration and confirmation in UV region. For distinguish between D & L isomeric forms. For identification & determination of purity of substance.

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