- Determine the zero of the polarimeter and the angle of rotation of polarised light at the wavelength of the D-line of sodium (l = 589.3 nm) at 20 ± 0.5 °C.
- Determine the zero of the apparatus with the tube closed; for liquids the zero is determined with the tube empty and for solids filled with the prescribed solvent. Carry out at least three measurements and calculate the average.
- Measurements of optical rotation are made in a 1.0-dm tube at 589 nm at the specified temperature in the chromatogram.
- Use the same cell for sample and blank
- Temperature, which applies to the solution or the liquid under test, should be maintained within
0.5 of the stated value.
- Prepare the sample solution as prescribed in monograph.
- Input the sample concentration in the polarimeter’s specified software data to determine the specific optical rotation as per the following equation:
or = the specific rotation at wavelength 589 nm at20 C or 25 C.
a =angle of rotation in degrees read at temperatures as prescribed in monograph
l = Path length in decimeters of the polarimeter tube “Constant”
c = The concentration of the analyte in g per 100 mL.
- Place the cell so that the light passes through it in the same direction each time.
- Measure the sample solution at temperatures as prescribed in monograph corrected the reading of the same tube with a solvent blank is used.
- The average of the measurement no fewer than three times.
- Note: 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 Determination is specified.
- Note: Optical rotation of solutions should be determined within 30 min of preparation.
- The specific optical rotation is calculated expressing dextrorotation and laevorotation designated by (+) and (–) respectively.
