The refractive index (n) of a substance is the ratio of the velocity of light in air to the velocity of light in the substance. It is valuable in the identification of substances and the detection of impurities.
The Refractometer Principle is the refractometer measures the range of refractive index for those Pharmacopeial materials for which such values are given.
The values for the refractive index given in this Pharmacopeia are for the D line of sodium (doublet at 589.0 nm and 589.6 nm). Most instruments available are designed for use
with white light but are calibrated to give the refractive index in terms of the D line of sodium light.
Refractometer Principle & Refractometer SOP
The purpose of Refractometer SOP is that the Refractometer is working properly and to use it correctly.
It is applicable for accurate measurement of the refractive Index in the Quality Control Department. It is valuable in the identification of substances and the detection of impurities.
Quality Control Manager
- “LOCK” knob
- “ADJUSTMENT” Knob
- “DISPERSION FACTOR” knob
- The lid of the Incident light.
- The lid of Refracted Light
Place the instrument on a flat surface and protect it against intense heat.
Before starting the operation check that light apertures should face intense light for a precise view of dark shadow.
Rotate the Knob named LOCK anticlockwise to open the sample port.
Clean the sample port first with water and then with methanol. Clean the surface with tissue or any other soft absorbent.
Put about 0.2-0.5ml sample and close down the lid and then the knob named LOCK clockwise to the maximum.
Before taking the readings make sure that the lid of the incident light is open and that of refracted light is closed.
Note the readings through the eyepiece. To get a refractive Index rotate the ADJUSTMENT knob until exactly the half circle in the eyepiece becomes dark.
If the margins of the dark shadow are not sharp, rotate the dispersion factor knob to get sharp borders of the black shadow cutting the half circle in the eyepiece.
Not down the reading from the scale through the eyepiece.
Corrosive Liquid should be placed carefully on the sampling surface and in small amounts so that it does not touch the other body part.
The sampling surface should be washed thoroughly after each sample with water and then with methanol and then it should be dried with tissue or any other clean absorbent.
7. Refractometer Calibration Procedure
The refractive index of purified water is 1.333, and this value helps us in calibrating our instrument.
Place the purified water as a sample and note down the value of the refractive index. Make corrections if necessary and record them on the calibration Record.
The refractometer shall be further calibrated against the following reference standards
|Name of Reference Standard Reagent||Standard Refractive index value|
|Carbon Tetrachloride at 20°C||1.4600 -1.4610|
|Toluene at 20°C||1.4940-1.4970|
|Distilled water at 20°C||1.3320-1.3330|