Polarimetry

POLARIMETRY

1. POLARIMETRY Presented By: G.T.ROOPESH M.PHARM Associate Professor Dept. Of Pharma.Chemistry BCP-ATP EMAIL ID: [email protected]

2. CONTENTS Introduction THEORY PLANE POLARIZED LIGHT OPTICAL ACTIVITY (THEORY) Factors Affecting OPTICAL ACTIVITY Instrumentation POLARIMETER Applications POLARIMETRY

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. 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 Polarised Light. NICOL Prism – Iceland Spar {Suitably CUT) Calcite ( CaCO 3 form ) (or) Polaroid

5. 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

6. OPTICAL ACTIVITY Definition : It Has find 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

7. The Rotatory Power of a given solution is generally expressed as specific rotation . It is the number of degress of rotation of plane polarized light produced by one gram of the substance per ml. The measurements is carried out at temp using sodium light. The Specific rotation can be Calculated by the following relation: [α] = specific rotation, T = temperature, λ = wavelength, θ= optical rotation, c = concentration in g/100ml , l = optical path length in dm.

8. Types of molecules analysed by Polarimetry: Molecule must be Optically active. Optically Active molecule contain asymmetric carbon atom. Asymmetric carbon/ Chiral carbon

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

10. INSTRUMENTATION The instrument used to measure the angle of rotation of the plane polarized light is called “POLARIMETER” O p ti c a l a c ti v ity m a y be d e t e c t e d & m e asu r e d by an instrument → Polarimeter

11. 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. Components of Polarimeter

12. POLARIMETER

13. Jasco-p-2000-digital-polarimeter

14. APPLICATIONS Quantitative application : I f the s p e c i f ic r o t a ti o n o f sa m ple i s k no w n its concentration in the solution can be estimated. Qualitative application : O p t ical activ i ty is the o n l y para m e t e r available f or distinguishing between D and L isomeric forms. Saccharimetry : I mportant practical application of polarimetry D etermination of high conc. of sugars V isual saccharimeters called POLAROSCOPES