POLARIMETRY CIRCULAR DICHORISM POLARIMETERpptx

POLARIMERTY

1. Polarimetry Polarimetry is a sensitive, nondestructive technique for measuring the optical activity exhibited by inorganic and organic compounds. A compound is considered to be optically active if linearly polarized light is rotated when passing through it The amount of optical rotation is determined by the molecular structure and concentration of chiral molecules in the substance

2. 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.

3. The term Polarimetry may be referred as the study of the rotation of polarised light by transparent optically active substance. This is a type of qualitative and quantitative analytical technique as both identification and estimation of the compound can be done

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

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

6. OPTICAL ACTIVITY: When certain organic liquids,solutions (sugar) or quartz crystal are placed in the path of polarized light,the plane of polarisation is rotated. The property by virtue of which the plane of polarisation is rotated is known as optical activity and the substance with this property is called optically active substance.

7. Substances which rotate the plane of polarised light to right side (clockwise) are called dextro rotatory(+) while which rotate towards left (anticlockwise) are called levo rotatory(-). A mixture of these two varieties in equal proportions will be optically inactive and is called racemic form. Example:lactic acid.

8. The 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

9. The Rotatory Power of a given solution is generally expressed as specific rotation. It is the number of degree 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:

10. SPECIFIC ROTATION: It is defined as the rotation produced by a solution of length 10cm & unit concentration (1gm/ml) for given wavelength of light at the given temperature.It is denoted by α.

11. Circular dichroism (CD) Circular dichroism spectroscopy is generally used to determine the secondary and tertiary structure of proteins. Its principle is based on differential absorption of left- and right-handed polarized light. To be detected by CD, the molecule should be asymmetrical; hence, the molecule should have one or more chiral chromophore. As optically active molecules absorb left- and right-handed circular polarized light differently, it becomes the basis of determining the biomolecule. There are different types of CD techniques depending upon the scanning spectrum range. Protein secondary structure is determined by UV CD technique. Similarly, vibrational CD and IR CD are used to study the structure of small organic molecules, proteins, and DNA, respectively

12. Electromagnetic radiation consists of oscillating electric and magnetic fields perpendicular to each other and the direction of propagation. Most light sources emit waves where these fields oscillate in all directions perpendicular to the propagation vector. Linear polarized light occurs when the electric field vector oscillates in only one plane. In circularly polarized light, the electric field vector rotates around the propagation axis maintaining a constant magnitude. In linear polarized light the direction of the vector stays constant and the magnitude oscillates. In circularly polarized light the magnitude stays constant while the direction oscillates.

13. 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.

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

15. applications for polarimetry are found in industry, research institutes and universities as a means of: Isolating and identifying unknowns, crystallized from various solvents or separated by HPLC. Evaluating and characterizing optically active compounds by measuring their specific rotation and comparing this value with the theoretical values found in literature

16. Polarimetric method is a simple and accurate means for determination of structure in micro analysis of expensive and non-duplicable samples. It is employed in quality control, process control and research in the pharmaceutical, chemical,essential oil, flavor and food industries. It is so well established that the United States Pharmacopoeia and the Food & Drug Administration include polarimetric specifications for numerous substances.