POLARIMETRY

POLARIMETRY Presented By -

Mr. Shaise Jacob

Faculty

Nirmala College of Pharmacy

Muvattupuzha, Kerala

India

Email – jacobshaise@gmail.com

• The term Polarimetry may be defined as the study of the rotation of polarised light by transparent substance.

• Optical rotatory power is useful for »

• Qualitative analysis

• Quantitative analysis

• Elucidation of chemical structures

• An ordinary light usually vibrates in all the planes → UNPOLARISED LIGHT

• The vibrations may all be restricted to one direction only, in the perpendicular plane → PLANE POLARIZED LIGHT

• Unpolarised light gets converted into a plane-polarized light by simply passing it through a lens called a NICOL Prism. (after William Nicol – the inventor)

• NICOL Prism – Iceland Spar

Calcite ( CaCO3 form )

(or) Polaroid

• 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

THEORY• An optically active substance is one that

rotates the plane of polarized light• (1) Lactic acid

• Latin : Dexter = right

designated by ‘d’• Latin : Laevus = left

designated by ‘l’

OPTICAL ACTIVITY When a certain organic liquids, solutions

(sugar) or quartz crystals are placed in the path of plane polarized light, the plane of polarization is rotated

Magnitude of rotation depend upon Nature of the substance Length of liquid column Conc. Of the solution Nature of the solvent Temperature of the solution WL of the light used

The rotatory power of a given solution is generally expressed as Specific rotation

a – observed angle of rotation

L – length in decimeters

C - grams of substance in 100ml of solution

INSTRUMENTATION Optical activity may be detected & measured

by an instrument → Polarimeter

• Light source – Sodium vapor lamp• Analyzer – another Nicol prism aligned to

intercept the linearly polarized ray as it emerges from the sample solution

Determination of optical activity of Pharmaceutical substances

Optical rotationSpecific optical rotation

noting the angle through which the plane of polarization is rotated.

Applications IdentificationDetermination of O.A compoundsQuantitative – sugar industry (sucrose)O.A is the only one parameter, for

distinguishing b/w D & L isomeric forms

SACCHARIMETRY» important practical application of polarimetry

» determination of high conc. of sugars

» visual saccharimeters called POLAROSCOPES