Refractometer - Operation, Calibration & Maintenance SOP

Operation, Calibration & Maintenance


To provide the procedure for operation, calibration and maintenance of Refractometer Mettler Refracto 30 PX. This instrument operating procedure also provides precautions to be taken and preliminary checks to be performed during operation.


Applicable to Refractometer Mettler Refracto 30 PX of Quality Control department.


°C        Degree Centigrade                                                                            

min     Minutes


Quality Control Chemists is responsible for the implementation of this Instrument Operating Procedures.


Manager Quality control is accountable for implementation and compliance of this Instrument Operating procedure.



1.1 Check and ensure that :

1.1.1 The instrument is clean and free from dust.

1.1.2  There should not be any deposition of the surface of the prism of the instrument if it is there clean with the soft cloth provided along with the instrument.

1.1.3 Before analysis, perform the adjustment of the measuring cell with purified water, it should come <0.0005. 


2.1 Measurement (Measure)

2.1.1 Procedure for proper measurement - Ensure that the prism and the measuring cell are clean before each measurement. Insufficient cleaning leads to remains on the prism and, therefore, incorrect results.

2.1.1 Check the sample for chemical resistance of the following materials :

·         Prism :                                          Glass (Refracto 30 GS : gold )

·         Measuring cell :                          Stainless steel SUS 316 (Refracto 30 GS : gold)

·         Housing :                                     PBT ( Polyester )

2.1.2 Ensure that the samples to be measured

·         Have reached more or less ambient temperature

·         Are homogeneous. Viscous and highly concentrated liquids have to be mixed        thoroughly before a sample is taken or a measurement is carried out.

·         Can be dissolved with a solvent suitable for cleaning the measuring cell

2.1.3 Adjust the instrument with water before performing the analysis.

3.0 Pipetting the sample onto the measuring cell.

3.1 Pipette the sample onto the measuring cell. The measuring cell has to be filled up to inner circle of the cell.

4.0 Dipping the measuring cell into the sample

4.1 Immerse the measuring cell completely in the sample.

Caution : Never immerse the instrument deeper into the sample than the indicated line (about 1.8 inch). The instrument is only resistant to splashed water.

5.0   Measurements

The procedure is dependent upon the setting in the menu

Measurements without temperature – compensation coefficient (α).

Configuration of sample identification and method of data storage.

Sample Name Sample identification 

A letter ( A… Z or space ) can be set for the identification of samples)

Mode Method of data storage.

Labo           By pressing the ok/measure key the result is saved and transferred ( pinter, PC).

Filed           By pressing the ok/measure key the result is saved Customer User-defined setting.

Memory in     Save results.

Auto                Save result automatically

Manu              result saved by pressing ok/measure key.

Memory out   Transfer result to PC or printer.

Auto                Save result automatically

Manu              result saved by pressing  key.

Measurements with temperature – compensation coefficient (α).

( nDT or conc. on the display ).

  • Press key until a previously saved temperature – compensation coefficient appears in the display, eg. a0= 0.091
  • Select the desired coefficient using the ↓ and ↑ keys.
  • Confirm the selected coefficient with the ok/measure key.
  • Press the ok/measure key to start the measurement. 
6.0     Saving the results

The instrument can save up to 1100 results internally. Each time a results is saved, the sample number increase by one. 

The Down symbol appears in the display : Savings all results automatically.

The instrument saves  all results automatically, After the measurement, as soon as the results are is saved, Ready appears on the display.

The Down symbol does not appear in the display : savings selected result manually

After the measurement, the result appears in reverse display Save the result :

- Press the ok/measure key.

Do  not save the result :

- Press the esc key.

Ready appears on the display and the instrument is ready for the next measurement.


7.0   Displaying and marking saved result

Display saved result

- Press the ← key.

  The sample number flashes and the symbol appears.

- Scroll through the saved result using the ↑ and ↓ key.

Marking results

For the identification of invalid or incorrect results or for marking a sample change.

- Select the desired sample number using the   ↑ and ↓ keys.

- Press the ok/measure key.

The selected sample number is marked with asterisk.

Note :The marking is removed if the sample has already been marked.

8.0         Printing and transferring results

Check the interface and peripheral device are configured properly

For PRN and RS interface, the infrared adapter must be connected to the printer / PC.

The procedure for printing and transferring result is dependent upon the setting in the menu as specified in the section measurements.

To transfer or print result, hold the instrument in the direction of the infrared adapter at a maximum distance of approx. 20 cm. 

The Up symbol appears in the display :  printing or transferring results automatically

Every display result is transferred automatically.

9.0 Adjustment

9.1 Adjusting the measuring cell with water

    Ensure that the measuring cell and surface of the prism are clean.

-          Transfer pure distilled water onto the measuring cell by means of the pipette which comes with the instrument. The measuring cell has to be filled up to the mark.

    Wait until the water has reached more or less ambient temperature .

    Press and hold the ↓ key, until CALIB (water) appears in the display

.-          The instrument adjust automatically ( duration : several seconds ). After adjustment is completed, the measured deviation from the theoretical value and Execute ? (No) appears.

Measured deviation < 0.0005

- Press the  ↓ or ↑ key.

- Execute ? (Yes) appears .

- Press the ok/measure key.

The adjustment is confirmed.

Measured deviation >  0.0005

- Check whether the measuring cell and the surface of the prism are clean.

-  Measuring cell and the surface of the prism are clean.

- Press the ↓ or ↑ key.

- Execute ? (Yes) appear.

- Press the ok/measure key.

-     Measuring cell and / or the surface of the prism are dirty.

-     Confirm Execute ? (No) by pressing the ok/ measure key.

-     Clean the cell and the surface of the prism and repeat the adjustment.

9.2    Adjusting the measuring cell with air

The Refractometer measures with specified accuracy if the measuring cell is correctly adjusted with distilled water. An adjustment with air is only necessary if the error message E-01 appears frequently during measurement or adjustment.

Preparing the measuring cell.

-          Clean the measuring cell and the surface of the prism thoroughly with a cleaning tissue. Wait until the surface of the prism is completely dry.


- Press the ↓ or ↑ key. Simultaneously. CALIB (Air) appears in the display. The instrument adjust the measuring cell automatically.

Adjustment is complete when CALIB (Air) disappears.

-  Adjust measuring cell with distilled water

If the error message E-01 appears in the display during the adjustment with air call inform service engineer.   

10.0    CLEANING :

10.1    Before cleaning, disconnect the balance from the power supply.

10.1.1 Do not use any aggressive cleaning agents or strong solvents.

10.1.2 Use a piece of cloth, which has been wet with a mild detergent (Soap) to clean the weighing pan and balance housing.

10.1.3 Make sure that no liquid enters the balance housing.

10.1.4 After cleaning, wipe down the balance with a soft, dry piece of cloth.

10.1.5 Carefully remove any sample residue / spilled powder by using a brush that is placed with the balance.


 Calibration frequency : Once in three months

Perform the calibration of the instrument by the following solvents:


Sr. No.


Refractive Index

Tolerance Limits



1.3330 at 20°C

1.3330 ± 0.001



1.3325 at 25°C

1.3325 ± 0.001



1.4603 at 20°C

1.4603 ± 0.001



1.4969 at 20°C

1.4969 ± 0.001

Temperature Calibration:

Procedure: Perform the temperature calibration using calibrated thermometer at a temperature at 20°C and 25°C using purified water maintained at 20°C and 25°C respectively.

Tolerance Limits: ± 0.5°C of the specified temperatures.

Note:   If instrument does not comply with any of the calibration parameters, then follow the relevant procedure of instrument breakdown.

MAJOR BREAKDOWN: Following are the major breakdown of the instrument

a)    Change in electronics


Manufacturers Operation Manuals

Indian Pharmacopoeia (IP).


Instrument calibration data sheet

Instrument calibration summary sheet


Master Copy                          : Quality Assurance

Control Copy                        : 10 : Quality control

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