POLARIMETRY
POLARIMETRY Presented By -
Mr. Shaise Jacob
Faculty
Nirmala College of Pharmacy
Muvattupuzha, Kerala
India
Email – [email protected]
• 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