Optical rotation determination method 0621 of the 2025 Edition of the Chinese Pharmacopoeia

Jiahang
In the formula, [α] represents specific curl;

D is the D line of the sodium spectrum.

t represents the temperature at the time of measurement, in ℃.

l represents the length of the measuring tube, dm.

α is the measured optical rotation;

d is the relative density of the liquid;

c represents the weight of the substance to be tested contained in each 100ml of the solution (calculated as dry or anhydrous substance), in grams.

The verification of a polarimeter can be carried out using a standard quartz polarimeter tube, and the reading error should comply with the regulations.

【 Notes

(1) Before each measurement, a blank correction should be made with a solvent. After the measurement, the correction should be conducted once again to determine if there is any change in the zero point during the measurement. If the optical rotation difference exceeds ±0.01 during the second calibration, it indicates that the zero point has changed, and the optical rotation should be remeasured.

(2) When preparing solutions and conducting measurements, the temperature should be adjusted to 20.0℃±0.5℃ (or the temperature specified under each variety item).

(3) The solution of the liquid or solid substance being tested should be fully dissolved, and the test solution should be clear.

(4) The optical rotation of a substance is related to factors such as the measurement light source, measurement wavelength, solvent, concentration and temperature. Therefore, when indicating the optical rotation of a substance, the measurement conditions should be specified.

(5) When it is known that the test sample has racemic effect or optical rotation conversion phenomenon, corresponding measures should be taken to specify the time for sample preparation and the interval time for filling the solution into the optical rotation tube for measurement.