GENERAL TESTING PROCEDURE
TITLE: OPTICAL ROTATION
GTP No.
GTP012 -00
Effective Date
Reference
USP / Ph.Eur.
Page No.
1.
1 of 2
PRINCIPLE:
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.
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.
2.
PROCEDURE:
2.1
Operate the Instrument as per current version of individual SOP
2.2
Prepare the test solution as per individual testing procedure and measure the optical
rotation/ Specific optical rotation.
2.3
Use the same cell for sample and blank.
2.4
Maintain the same angular orientation of the cell in each reading.
2.5
Place the cell so that the light passes through it in the same direction each time.
2.6
Calculate the optical rotation using the formula:
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
2.7
Unless otherwise mentioned in the individual testing procedure perform the Optical
rotation and specific optical rotation at 589nm and 25°C.
2.8
Where a photoelectric polarimeter is used, a single measurement, corrected for
the solvent blank, is made.
2.9 Where a visual polarimeter is used, the average of no fewer than five determinations,
corrected for the reading of the same tube with a solvent blank, is used.
2.10 Temperature, which applies to the solution or the liquid under test, should be
maintained within ± 0.5°C of the stated value.
GENERAL TESTING PROCEDURE
TITLE: OPTICAL ROTATION
GTP No.
GTP012 -00
Effective Date
Reference
USP / Ph.Eur.
Page No.
2 of 2
2.11 Unless otherwise specified, specific rotation is calculated on the dried basis
where
Loss on drying is specified in the monograph or on the anhydrous basis where
water is specified.
2.12 Optical rotation of solutions should be determined within 30 minutes of
preparation.
2.13 In the case of substances known to undergo racemization or mutarotation, care
should be taken to standardize the time between adding the solute to the
Solvent and introduction of the solution into the polarimeter tube.