SOP for Refractometer : Pharmaguideline

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SOP for Refractometer

Standard operating procedure of Refractometer to determine the refractive index of liquid samples.


To describe the procedure for operation and calibration of Refractometer.


This SOP is applicable for operation and calibration of Refractometer.


Officer/ Executive - Quality Control


Manager - Quality Control


5.1 Operations

5.1.1 Ensure that the instrument is free from dust.
5.1.2 Ensure that all the parts including eye lens, prisms and mirror are clean before the operation.
5.1.3 Place the instrument on a table where adequate light can be reflected through the mirror.
5.1.4 Open the prism lock and place few drops of the liquid testing sample at the temperature specified.
5.1.5 Allow the liquid to smear on the lower prism surface quickly close the prism lock.
5.1.6 Adjust the eyepiece cross wire with a knob by rotating it in a clockwise or anti-clockwise direction so that the sharp demarcation line passes through its center.
5.1.7 Sharp demarcation is produced in the form of a circle having half light & half dark portion.
5.1.8 A knob provided just above the prism can do fine adjustment.
5.1.9 Note down the reading from the scale with the help of the magnifier lens of the instrument.
5.1.10 Use thermometer and water jacket with tubes provided in the instrument whenever it is required.
5.1.11 Clean the instrument and keep under box when not in use.

5.2 Calibration

5.2.1 To achieve accuracy, the instrument should be calibrated against distilled water, which has a refractive index of 1.3325 at 25 °C against the reference liquids given below:
Carbon Tetrachloride: 1.4603
Toluene: 1.4969
Water: 1.3325
5.2.2 Frequency of calibration: Monthly.

5.3 Precautions

5.3.1 Proper handling of the instrument.
5.3.2 Temperature should be carefully adjusted and maintained since refractive index varies significantly with temperature.


6.1 SOP - Standard Operating Procedure
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