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SOP for Calibration of Volumetric Glassware

Glassware is commonly calibrated using a liquid of known, specific density, and an analytical balance. The procedure is to determine the mass of liquid the glassware will hold, and to divide this mass of liquid by the density of the liquid, obtaining the corresponding volume of liquid.

OBJECTIVE 
  • To provide a procedure for calibrating volumetric glassware. 
  • To ensure that the volumetric glassware performs satisfactorily to give consistent and accurate volumes all the time. 
  • To provide criteria to reject or dispose of defective glassware. 

SCOPE 
  • This procedure applies to the calibration of Volumetric Flasks, Conical Flasks, Beakers, Measuring Cylinder, Bulb Pipet, Graduated Pipettes and Burettes. 
  • This procedure applies to the calibration of all new volumetric and graduated glassware. 
RESPONSIBILITY 
  • It is the responsibility of the QC Analyst as assigned to carry out the calibration procedure fully. 
  • It is the responsibility of the Manager-QC to ensure that the procedure Is followed. 

PROCEDURE 
Frequency: This procedure shall be conducted after every six months. 
Accessories:
Thermometer 
Distilled water 
Weighing balance (Calibrated) 
Paper towel or equivalent 
Erlenmeyer flask or beaker. 

Calibration of Pipette 
  • Make sure the Pipette is clean before use. 
  • Rinse the interior by drawing a portion of the distilled water into the Pipette with the aid of suction bulb, and then Pipette until the entire inner surface has been wetted. 
  • Weigh an empty clean and dry receiving vessel (beaker /erlenmeyer flask) to the nearest 0.0001g on the analytical balance. 
  • Fill a 250ml beaker with distilled water. Record the temperature of water.
  • Use a Pipette filler to fill the Pipette to a level about 2cm above the line. 
  • Remove the Pipette filler and quickly place your forefinger on the end of the Pipette. Wipe off the lower stem and tip of the Pipette.  
  • By carefully releasing the pressure of your finger slightly, adjust the level of the water until bottom of the meniscus is exactly on the line, if you overshoot the line; simply apply suction again to refill the Pipette. 
  • Holding the Pipette vertically, allow the water to drain by gravity in the holding vessel. If any liquid remains in the top of the pipet, do not blow it out. This retained drop of liquid is accounted for in the calibration of the pipet. 
  • Weigh the receiving vessel with water from the Pipette and record.
  • Repeat the calibration at least twice. 
  • Record your results in computer situated in the Laboratory Instrument room. Access excel program and retrieve the ‘Calibration Template Pipette’ file. Enter temperature and the weights and the program will automatically calculate the tolerances. 
Calibration of a volumetric flask 
  • Permanently mark identification numbers to clean and dry, stoppered volumetric flasks and record. 
  • Weigh the clean and dry, stoppered volumetric flask to the nearest milligram on an analytical balance for volumetric flasks of 100ml or less, to the nearest 0.1g on a suitable scale for volumetric flasks of capacity more than 100ml. 
  • Insert a clean, dry funnel into the flask so that the stem extends below the calibration mark of the flask. Fill the flask with water whose temperature should be recorded.
  • Carefully remove the funnel, add water with a pipet until the bottom of the meniscus coincides with the calibration line. Ensure that no droplets remain above the mark. 
  • Stopper the flask and reweigh it. 
  • Empty and dry the volumetric flask in an oven set at 105°C and repeat steps twice. 
  • Enter the results of the weights on the computer situated in the Laboratory Instruments room using excel program and file name is ‘Calibration Template’ This program will automatically calculate the tolerance volumes. 

Calibration of Burette 
  • Ensure that the Burette is clean before use, if small droplets of water adhere to the inner surface of the Burette after delivering deionized water; the Burette is dirty and must be cleaned before proceeding further. 
  • Fill in the Burette with water whose temperature has been recorded and make sure that air bubbles are not trapped in the stopcock or tap. 
  • Drawing water from the Burette very slowly, lower the liquid level until the bottom of the meniscus just rests on the 0.00ml mark. Touch the tip to the wall of a beaker to remove any adhering drop. Wait for 10 minutes and recheck the volume. If the stopcock is tight, there should be no perceptible change in the meniscus. 
  • During this interval, weigh (to the nearest milligram) the receiving vessel and record.
  • Once tightness of stopcock has been established slowly transfer (at a rate of about 10ml/min) approximately 10ml of water to the receiving vessel. 
  • Touch the tip to the wall of the receiving vessel and stopper. Wait one minute, then record the apparent volume delivered from the buret to the second place after the decimal. 
  • Weigh the receiving vessel and its contents to the nearest milligrams and determine the mass of water delivered by difference. 
  • Subtract the apparent volume from the corrected volume. Thus differences are the correction that should be applied to the apparent volume to give the true volume.  
  • Starting again from zero mark, repeat the calibration this time, delivering about 20ml to the receiver following the procedure given above. Calibrate the buret delivering approximately 30, 40 and 50ml recording to the data on the report sheet.
  • Repeat the 10ml calibration until agreement between subsequent true values is within ± 0.02ml 
  • Record the correction factors. Then prepare a plot of correction factors (y – axis) which are to be applied to convert apparent volume (x – axis) of water delivered. The correction factors which must be applied to any apparent volume can be read from this graph. 

REVISION HISTORY 
Nil

ABBREVIATION: 
DM: Demineralized 
QA: Quality Assurance 
QC: Quality Control 

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