Polarimeter – Operation and Calibration Procedure

Standard Operating Procedure (SOP) for Operation and calibration of Polarimeter used to determine of optical rotation of raw material in Quality Control.

Procedure for Polarimeter – Operation and Calibration

1.0   Objective :

    • To lay down a procedure for operating and calibration of Polarimeter. It is used to determine the optical rotation of material.

2.0   Scope :

    • This SOP is applicable for operation and calibration of Polarimeter in Quality Control.  

3.0   Procedure – Polarimeter:

    • What is Optical Rotation ?

    • The optical rotation is the angle through which the plane of polarization is rotated when polarized light passes through a layer of a liquid. 
    • Optical rotation is the effect which is determined by the concentration of chiral molecules and their molecular structure in a substance
    • Operation Procedure for Polarimeter:

    • Ensure that equipment & tube is clean.
    • Check the calibration due date.
    • Set up the instrument on the bench with the analyzer head facing the operator, an illuminated sodium lamp is attached with equipment through a bracket.
    • Switch ON the mains.
    • Switch ON the Sodium vapour lamp by pushing the switch of transformer downward. The red indicator will glow on transformer.
    • Wait for five minutes so that Sodium vapour lamp gets illuminated completely.
    • The position of Sodium vapour lamp is such that the field can be seen clearly while viewing through lower eyepiece.
    • Adjust the lower & upper eye piece & focus it by sliding it towards your eye or away from your eye to view the clearly.
    • After focusing the upper eye piece you will see the scale graduation & a vertical line called reference line.
    • Rinse the tube with the solvent used and fill the tube with the solvent in such a manner that there should not be any air bubble.
    • Place the tube in the cabinet and close it.
    • Now see through the lower eye piece and match the colour shade to similar in both section by rotating the knob placed on the opposite to eye piece.
    • Take the reading by viewing through upper eye piece.
    • If the reference line do not concide with the scale then adjust with micrometer drum knob.
    • Take the five readings.

    • Now rinse the tube with the solution and fill the tube with the liquid / prescribed solution and take reading following the procedure given above.
    • Take the reading in + or -.
    • Deduct the reading of solvent from reading of liquid/sample and calculate the specific optical rotation.
    • After completion of work open the cabinet, remove the tube and clean it thoroughly.
    • Switch off the Sodium vapor lamp.
    • Enter the details in Instrument log.
  • Calibration Procedure of Polarimeter:

    • Operate the equipment as per SOP.
    • Weight accurately 50 g sucrose (previously dried) and transfer in 100 ml volumetric flask.
    • Add 50 ml water (milli Q), shake well to dissolve and make up the volume with water (milli Q) (solution A).
    • Rinse the tube (1-dm) with water (milli Q) and filled the tube with water (milli Q) after maintaining the temperature 25 ±1ºC.
    • Set the null point with the help of knob adjustment and note the reading up to two decimal place with the help of linear and outer side.
    • Rinse the tube with sucrose solution (A) and follow the steps in SOP and measure the angle of rotation.
    • Similarly prepare solution of 40, 30, 20 and 10g/ 100 ml by diluting 20.0 ml, 15.0 ml, 10.0 ml, and 5.0 ml of solution (A) to 25.0 ml with water (milli Q).
    • Measure the angle of rotation following steps of SOP and record the observation Annexure I.
    • Take average of five readings for each concentration.
  • Acceptance criteria for Polarimeter Calibration:

Concentration (g/100ml)                  Angle of rotation (+) at 25ºC

10                                                                                   6.66° ± 0.5

20                                                                                 13.30°± 0.5

30                                                                                 19.93° ± 0.5

40                                                                                 26.53°± 0.5

50                                                                                  33.11° ± 0.5

    • Enter the details in Annexure I.
    • Prepare the calibration tag and affix it on the Polarimeter.
    • Enclose the old calibration tag with the record and don’t throw it.
    • If the variation is not within the specified tolerance limits:

    • Inform the Department Head.
    • Do not use equipment until all errors are rectified. After rectification, again calibrate the equipment & record the observation.
    • Frequency: 6 Months ± 3 days.
    • Important:

    • Fill the tube in such a manner that there should not be any air bubble.
    • The temperature of solvent / solution should be 25°C ±1°C.
    • Ensure that the solution is clear.
    • Take five readings for each operation of Polarimeter.
    • For any deviation in equipment inform to service engineer.
    • For more details refer instruction manual.

Annexure I: Calibration Record of Polarimeter

Format for Calibration of Polarimeter

Make                         : ……………….                                  Eq. No.                                   : ……………….

Model No.                 : ……………….                                  Calibration Frequency         : 6 Months ± 3 days   

Calibration Due on: ……………… 

Batch No. of Sucrose: ……………….

Stock Solution A: Dissolve ………………….. g. Sucrose in 100.0 ml  (…………ml ) water (Milli Q)

 Length of Polarimeter Tube: 1 dm  Light Source : Sodium Light  (589.3 nm)
Volume Taken


Diluted to Volume


Concentration (%) Angle of Rotation at 25°C Acceptance criteria


Observed Average
5.0 25.0 10 +6.66±0.5
10.0 25.0 20 +13.30±0.5
15.0 25.0 30 +19.93±0.5
20.0 25.0 40 +26.53±0.5
Stock Solution A ………. 50 +33.11±0.5

Remarks: The observed values comply / does not comply the acceptance criteria and the equipment can be / cannot be used for routine analysis.

Next calibration due date : …………………..    

4.0   Reference(s) – Polarimeter SOP

    • Manufacturer manual
    • Chapter No. 2.4.22 of IP 2014


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