OPTICAL ROTATION

1. PRINCIPLE:
2. OPTICAL ROTATION: Substances that may show optical rotatory power are chiral. Those that rotate light in a clockwise direction as viewed towards the light source are dextrorotatory, or (+) optical isomers. Those that rotate light in the opposite direction are called levorotatory or (–) optical isomers.
3. SPECIFIC ROTATION: The specific rotation of a chemical compound [α] is defined as the observed angle of optical rotation α, when plane-polarized light is passed through a sample with a path length of 1 decimeter and a sample concentration of 1 gram per 1 deciliter. The specific rotation of a pure material is an intrinsic property of that material at a given wavelength and temperature. 
4. PROCEDURE:
5. 2.1     Operate the Instrument as per current version of individual SOP
6. 2.2     Prepare the test solution as per individual testing procedure and measure the optical rotation/ Specific optical rotation.
7. 2.3     Use the same cell for sample and blank.
8. 2.4     Maintain the same angular orientation of the cell in each reading.
9. 2.5     Place the cell so that the light passes through it in the same direction each time.
10. 2.6     Calculate the optical rotation using the formula: 
11. where [α] is the specific rotation at wavelength, t is the temperature, a is the observed rotation in degrees, l is the pathlength in decimeters, and c is the concentration of the analyte in g per 100mL
12. 2.7     Unless otherwise mentioned in the individual testing procedure perform the Optical rotation and specific optical rotation at 589nm and 25°C.
13. 2.8     Where a photoelectric polarimeter is used, a single measurement, corrected for the solvent blank, is made.
14. 2.9    Where a visual polarimeter is used, the average of no fewer than five determinations,
15.  corrected for the reading of the same tube with a solvent blank, is used.       
16. 2.10   Temperature, which applies to the solution or the liquid under test, should be  
17. maintained within ± 0.5°C of the stated value.
18. 2.11   Unless otherwise specified, specific rotation is calculated on the dried basis where  
19. Loss on drying is specified in the monograph or on the anhydrous basis where water is specified.
20. 2.12   Optical rotation of solutions should be determined within 30 minutes of preparation.
21. 2.13   In the case of substances known to undergo racemization or mutarotation, care  
22.  should be taken to standardize the time between adding the solute to the Solvent  and introduction of the solution into the polarimeter tube.

General testing procedure,optical, rotation