Table of Contents
1.0 PURPOSE:
1.1 To lay down a procedure for operation and calibration of Refractometer.
2.0 SCOPE:
2.1 This procedure is applicable for operation and calibration of Refractometer used in the Quality Control Laboratory.
3.0 RESPONSIBILITY:
3.1 Chemist / Officer / Executive Quality control / Designee are responsible to perform the activity as per procedure.
3.2 Head -Quality control / designee is responsible to ensure proper execution of the procedure.
4.0 ACCOUNTABILITY:
4.1 Head -Quality Control
5.0 DEFINITIONS, PRECAUTIONS & DISTRIBUTIONS:
5.1 Definitions: Not applicable
5.2 Precautions:
5.2.1 Instrument prism should be checked after every analysis for cleanliness. Any sticky material should be immediately cleaned with the proper solvent (In which sample is soluble and then clean with the acetone) Clean the electrode with purified water and soft tissue paper.
5.2.2 For light adjustment mirror plate should be cleaned with a cloth.
5.2.3 Required temperature should be maintained as the refractive index of substance varies significantly with slightly change in temperature.
5.3 Distributions:
5.3.1 Master copy – Documentation Cell (Quality Assurance).
5.3.2 Controlled copies – Quality Control.
6.0 PROCEDURE:
6.1 Operation:
6.1.1 Ensure that instrument is clean and free from dust.Switch on the main power supply.
6.1.2 Press the power switch of the main unit placed at the left side button. The power is supplied to it with indication of mode, number (nD or Brix %) corresponding to the measurement knob and temperature in the display.
6.1.3 For measuring the refractive index of sample, follow the following point.
6.1.4 Press SELECT key and select mode indication “nD” Le refractive index and then press the SET key.
6.1.5 Turn the Prism open-shut handle to open the secondary prism carefully. Clean the main and secondary prism surface and then apply a few drops of sample on to the main prism. Close the secondary prism.
6.1.6 Observing through the eye piece, turn the measurement knob to match the boundary line with the intersection point of the cross line.
6.1.7 When the colour blurs on the boundary line turn the colour compensation knob to remove the colour blurring.
6.1.8 The value indicate as the boundary line crosses the intersection point of the cross line in the measurement value of the sample.
6.1.9 After completion of test, clean the prism with water and dry with tissue paper.
6.1.10 Switch off the instrument after analysis.
6.2 Calibration of Refractometer.
6.2.1 For calibration, use the following solvents at the stated temperature.
6.2.2 Check the Refractive Index of Distilled Water at 20±0.5°C
6.2.3 Check the Refractive Index of Carbon Tetrachloride and Toluene at 20±0.5°C.
6.2.4 Check whether the Refractive Index of the individual solvents fall within limits as stated in Acceptance criteria of refractometer.
6.2.5 Record the results on Calibration Record as per Annex.
6.2.6 Calibration Frequency: Half Yearly, Tolerance limit – 15 days.
6.2.7 ACCEPTANCE CRITERIA of Refractometer
| Reference liquid | Tolerance Limit for Refractive Index |
| Distilled water | 1.3330 ± 0.0001 at 20°C |
| Carbon Tetrachloride | ± 0.0001 at 20°C |
| Toluene | 1.4969 ± 0.0001 at 20°C |