Operation and Calibration of Refractometer SOP (Make-Rajdhani)

SOP for Refractometer Calibration as per Indian Pharmacopoeia.

  • SOP Covers below points:
    • Precautions
    • Operation of Refractometer
    • Calibration of Refractometer
    • Refractometer Calibration format
  • To provide a procedure for Operation and Calibration of Refractometer.
2.0 SCOPE :
  • This procedure is applicable to RAJDHANI make Refractometer Instrument.
  • Quality control Chemist and above
  • Quality Control Head

Refractometer is a laboratory device which measure the degree to which the light changes direction, called the angle of refraction/ Refractive index. 

The instrument is used for checking of Refractive Index of transparent liquid having Refractive Index between 1.300 to 1.700.


  • Clean all parts of Refractometer including eye lens, prism and mirror before and after use with the help of tissue paper.
  • Keep the instrument in its wooden box after use.
  • The temperature should be carefully adjusted and maintained since the refractive index varies significantly with temperature.


  • Open the wooden box and carefully remove the instrument from box.
  • Place the instrument on table where adequate light can be reflected through mirror.
  • Open the prism lock and place 2-3 drops of sample onto the lower prism using a clean pipette, making sure that you do not touch the prism with the pipette.
  • Allow the liquid to smear on lower prism surface quickly, close the prism lock.
  • Adjust the eye piece cross wire with the knob by rotating it in a clockwise or anticlockwise direction so that the sharp demarcation line passes through center.
  • In case of any difficulties for making these adjustments or uneven interfaces or blobs of black colour is seen, that is probably because enough sample on the PRISM is not available.
  • If a rainbow of colours is observed, turn the Fine Adjust knob until a sharp interface is obtained.
  • If observation is close to the index of refraction of sample, the view in the eyepiece shows a dark region on the bottom and a lighter region on the top.
  • Once a crisp demarcation between the light and dark regions is reached, turn the handwheel on side to place the borderline exactly on the center of the crosshairs as shown below,

  • Sharp demarcation is produced in the form of circle having half light and half dark portion.
  • A knob provided just above the prism can do fine adjustment.
  • Note down the reading from the scale with the help of magnified lens of the instrument as below,
    • The left side of scale indicate Refractive Index Range of scale is 1.300 to 1.700.
    • The right side scale (sugar at 20° 1996) is not used here as it indicate the concentration of sugar in water.
    • View the scale and read your R.I. where the horizontal line crosses the right scale.
    • The example shown here has a refractive index of 1.342 .
    • The refractive index is unit less number.

  • Open the prism and wipe the upper and lower plates with a tissue moistened with acetone. Leave open to dry.


  • Observe the refractive index of the following liquids which is as per Indian Pharmacopoeia.
Reference LiquidTemperature of liquidStandard Refractive IndexLimits
Distilled Water25°C1.33251.332 – 1.334
Toluene (Extra Pure grade)20°C1.49691.495 – 1.497  
Carbon Tetrachloride (Analytical Reagent grade)20°C1.46031.459 – 1.461   

  • FREQUENCY : Quarterly
 AbbreviationExpanded form
°CDegree Celsius
R.I.Refractive index

Annex. No.         Title
01 Calibration of Refractometer

  • Manual of Refractometer
  • Indian Pharmacopoeia



Annex. No. 01 Calibration of Refractometer