LimsPulse
Physical testing

Polarimeter

Measures how much a solution of a chiral substance rotates the plane of polarised light. The result is used to calculate specific optical rotation, an identity and purity test for many APIs.

  • Pharmaceutical
  • Food & sugar
  • Flavours & fragrances
  • Chemicals
  • Academic research
Photo of a Polarimeter
Photo: Gingkoaceae, CC BY-SA 4.0 (cropped), via Wikimedia Commons
Follow your site SOP
This is a typical operating sequence for learning. Your instrument model and approved SOP take precedence.
STAGE 1

Before you start

  1. 1Check the calibration label and that the daily check with a quartz plate (if required) has passed.
  2. 2Switch on and allow the lamp and temperature control to stabilise (often 15–30 minutes).
  3. 3Set the measuring temperature and wavelength stated in the monograph.
  4. 4Clean the tube and windows; check the windows are not scratched.
  • Never use a cracked or scratched tube; window strain itself rotates light.
STAGE 2

Blank / zero

  1. 1Fill the tube with the solvent used for the sample, avoiding bubbles.
  2. 2Place the tube in the instrument with the same orientation you will use for the sample.
  3. 3Take the reading and zero the instrument, or record the blank value for subtraction.
  • Bubbles in the light path give unstable or wrong readings; tilt the tube so bubbles move into the bubble trap.
STAGE 3

Measurement

  1. 1Rinse the tube two or three times with the sample solution, then fill it.
  2. 2Place the tube in the instrument and wait for the temperature to reach the set value.
  3. 3Take at least five readings, or the number your SOP asks for, and record the mean.
  4. 4Subtract the blank, if it was not zeroed, and calculate the specific optical rotation.
  • Filter turbid solutions before filling; particles scatter light.
  • Measure within the time stated in the monograph; some substances change rotation in solution (mutarotation).
STAGE 4

After use

  1. 1Empty the tube, rinse with solvent and water, and dry it.
  2. 2Store tubes and quartz plates in their cases.
  3. 3Complete the instrument log.
In LimsPulse · Calibration Management

Keep every Polarimeter in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.

See how