SOP for Refractometer Calibration as per Indian Pharmacopoeia.
- SOP Covers below points:
- Precautions
- Operation of Refractometer
- Calibration of Refractometer
- Refractometer Calibration format
1.0 OBJECTIVE :
- To provide a procedure for Operation and Calibration of Refractometer.
2.0 SCOPE :
- This procedure is applicable to RAJDHANI make Refractometer Instrument.
3.0 RESPONSIBILITY :
- Quality control Chemist and above
4.0 ACCOUNTABILITY:
- Quality Control Head
5.0 PROCEDURE :
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.
5.1 PRECAUTION
- 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.
5.2 OPERATION
- 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.
5.3 CALIBRATION
- Observe the refractive index of the following liquids which is as per Indian Pharmacopoeia.
| Reference Liquid | Temperature of liquid | Standard Refractive Index | Limits |
| Distilled Water | 25°C | 1.3325 | 1.332 – 1.334 |
| Toluene (Extra Pure grade) | 20°C | 1.4969 | 1.495 – 1.497 |
| Carbon Tetrachloride (Analytical Reagent grade) | 20°C | 1.4603 | 1.459 – 1.461 |
- FREQUENCY : Quarterly
6.0 ABBREVIATIONS:
| Abbreviation | Expanded form |
| °C | Degree Celsius |
| R.I. | Refractive index |
7.0 ANNEXURES:
| Annex. No. | Title |
| 01 | Calibration of Refractometer |
8.0 SOP REFERENCES
- Manual of Refractometer
- Indian Pharmacopoeia
END OF THE SOP
ANNEXURES :
Annex. No. 01 Calibration of Refractometer
