Polarimetry

Introduction
Plane Polarised Light
Optical Activity
Theory of Optical Activity
Polarimeter
Applications

1. POLARIMETRY PHARMACEUTICAL ANALYSIS CHOTHISH JAYARAM 3 RD PHARMD

2. Introduction Plane Polarized Light Optical Activity Theory of Optical Activity Polarimeter Applications

3. INTRODUCTION Polarimetry is one of the important instrumental methods employed in analysis. This measures the rotation of the polarized light as it passes through an optically active compound. This technique involves the measurement of change in the direction of vibration of polarized light when interact with an optically active compound. A substance is said to be optically active if it rotates the plane of the polarized light.

4. B. PLANE POLARISED LIGHT • According to wave theory of light, an ordinary ray light is considered to be vibrating in all planes at right angle to the direction of propagation. If this ordinary ray of light is passed through a Nicol prism, the emergent ray has its vibration only in one plane. This light having wave motion in only one plane is known as Plane Polarized Light. • A plane polarized light which consists of two components of fixed magnitude rotating in opposite directions to one another; • The right circulatory polarized light • The left circulatory polarized light • Plane polarized light is the vector sum of these two components • NICOL Prism – Iceland Spar Calcite ( CaCO3 form ) (or) Polaroid

5. a. Linearly polarized light b. Left circulatory polarized light c. Right circulatory polarized light

6. C. OPTICAL ACTIVITY Optical activity  is the ability of a chiral molecule to rotate the plane of plane- polairsed light, measured using a  polarimeter .  A simple polarimeter consists of a light source, polarising lens, sample tube and analysing lens. It was found that magnitude of rotation depend upon the following factors: Nature of Substance Length of liquid column ( l ) through which light passes. Concentration of the solution. Nature of the solvent. Temperature of the solution (t) Wavelength of the light used • Types of molecules analyzed by Polarimetry: Molecule must be Optically active. 2. Optically Active molecule contain asymmetric carbon atom. :

7. D. Theory of Optical Activity • An optically active substance is one that rotates the plane of polarized light Example: Lactic acid Dextro right designated by ‘d’, (+), clockwise Levo left designated by ‘l’, (-), counter clockwise

8. INSTRUMENTAION A polarimeter is an instrument which measures the angle of rotation by passing polarized light through an optically active (chiral) substance. To measure optical rotation, a Light Emitting Diode (LED) produces a beam of ordinary light. This light first passes through a polarizer (polarization filter) in order to obtain a defined orientation of the plane of polarization. The polarized light then passes through the sample cell. If the sample is optically active, the plane of polarization becomes rotated. The light with the rotated plane of polarization passes through an analyzer , which is a second polarization filter. The polarimeter rotates the first polarizer until the photo receiver measures a transmission minimum. If the sample is optically inactive, polarizer and analyzer are now oriented perpendicular to another. If the sample is optically active, the polarimeter rotates the polarizer until the plane of polarization behind the sample cell is again perpendicular to the polarization plane of the analyzer . The resulting degree of rotation is a direct measure of the optical rotation of the sample. The correct wavelength for the measurement is precisely selected by an interference filter positioned in the beam in front of the photo receiver.

9. In case of a Modular Circular Polarimeter (MCP) ,  the first polarizer is fixed. The polarized light additionally passes through electromagnetic coils (Faraday modulator) to further enhance the angular resolution. Thereby an oscillation is superimposed onto the plane of polarization by means of the Faraday effect. The Faraday modulator is located in front of the sample cell (see fig. 6). After the polarized light’s transition through the sample cell, the analyzer is rotated automatically until the transmission minimum is reached. • Light source – Sodium vapor lamp • Analyzer– another Nicol prism aligned to intercept the linearly polarized ray as it emerges from the sample solution • A polarimeter consists of a polarized Light source – Sodium vapor lamp, Polarizer –quartz prism material and Analyzer – Nicol prism aligned to intercept the linearly polarized ray as it emerges from the sample solution, a graduated circle- to measure the rotation angle, and sample tubes.

10. E.APPLICATION Pharmaceutical industries Polarimetry is used in pharmaceutical industries for purity control and determination of concentration of substances according to the requirements of the European and American Pharmacopeia by measurement of both specific and optical rotation. Alkaloids : cocaine, codeine, nicotine, morphine sulphate, etc. Amino acids : asparagine, glutamic acid, etc. Organic compounds : ascorbic acid, menthol, camphor, etc.          Others : steroids, antibiotics, serums,   vitamins, etc.   2.Medicine   Research of sugar and albumin in urine Hormone research Enzymology and toxicology research

11. Chemical Industries Purity control and measurement of concentration, identification, and characterization of compounds, such as: Organic fluids Biopolymers Synthetic polymers Organic polymers Research applications Analysis of optically active compound structure analysis Determination of configuration changes of solved macromolecules Monitoring changes in concentration of an optically active component in a reaction mixture, as in enzymatic scission Distinction of optical isomers Investigating kinetic reactions by measuring optical rotation as a function of time Analyzing molecular structure by determining optical rotation dispersion

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