Calibration procedure for volumetric glassware

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Calibration of glassware before use is important as it ensures that the quality of measuring glassware by comparison of their physical parameters with standards of high accuracy.

Always use the class ‘A’ glassware along with its certificate for analytical testing.

If any glassware is not used for two years from the date of receipt, then it must be first Calibrated by the analyst then will be released for regular use.Calibration is required only for those glassware which are used for the quantitative measurements such as volumetric flask, volumetric pipette, burette, volumetric cylinder.

Tools required for calibration: calibrated analytical weighing balance Class’A’ beaker of required capacities or any other suitable glassware for transferring the measured liquid, calibrated thermometer.

Calibration of volumetric flasks :

  • Before calibration, clean and dry the flask to be calibrated.
  • Weigh the empty flask and record the accurate weight of flask.
  • Take distilled water at room temperature and ensure that water attains temperature equilibrium with room temperature by keeping at room temperature for half an hour.
  • Fill the flask with distilled water up to the calibration mark, taking care that no water droplets remain on the neck of the flask or above the calibration mark.
  • Note the temperature of distilled water used and room temperature.
  • Weigh the filled flask and record the weight, Subtract the empty weight of volumetric flask and record the weight.
  • Convert the weight of water at room temperature into volume of water at 27°C as given below:

Vt  =  W x Ft

Where,  Vt  = Volume of water at the observed temperature t °C

W  = Wt of water at the observed temperature t °C

Ft  = Factor (The value of which can be found out from the following Table.)

 

      t °C  (Water) Ft t °C  (Water) Ft
            20 1.0028 28 1.0048
            21 1.0030 29 1.0051
            22 1.0033 30 1.0054
            23 1.0035 31 1.0057
            24 1.0038 32 1.0060
            25 1.0040 33 1.0064
            26 1.0043 34 1.0067
            27 1.0045 35 1.0070

 

Calculate the  volume  of  water  at  27°C   from following equation:

V27  = Vt (1 + 0.0001 (27 – t °C  air) ) Where, 0.0001 = co-efficient of thermal expansion of borosilicate glass.

In case off small temperature difference,  V27  = Vt

      TOLERANCES ON CAPACITY FOR VOLUMETRIC FLASKS

Flask Capacity (ml) 5 10 25 50 100 200 250 500 1000
Class A Tolerance +/-(ml) 0.02 0.02 0.03 0.04 0.06 0.1 0.1 0.15 0.2


Calibration of bulb pipettes:

  • Before calibration, clean and dry the pipette to be calibrated.
  • Weigh a clean, dry beaker of suitable capacity i.e. in accordance with the capacity of pipette to be calibrated and record its weight.
  • Fill the pipette under calibration by suction of distilled water, having temperature equilibrium with the room temperature, up to the level of 2 – 3 cm above the graduation line. Note the room temperature and the temperature of water.
  • Wipe the outside of delivery jet of pipette with tissue paper. Hold the pipette in vertical position and allow draining the water until the base of the meniscus is set accurately against the graduation mark.
  • Allow the water to flow down freely in tared receiving beaker, until out flow completely ceases. Note down the out flow time.
  • Maintain the pipette and receiver in the same position for 15 seconds.
  • Weigh the receiver with water collected in it. Convert the weight of water at room temperature into volume of water at 27°C by using same equation give above for volumetric flask.
  • Check the results against the tolerance given in following table.
Bulb Pipettes 1 2 5 10 20 25 50 100
Class A Tolerance +/- (ml) 0.01 0.01 0.02 0.02 0.03 0.03 0.04 0.06
Class A Delivery time range (Seconds) 5-10 5-10 10-25 15-25 15-30 20-35 25-40 30-50

 

      Calibration of burettes:

  • Before calibration, clean and dry the burette to be calibrated.
  • Weigh a clean, dry beaker of suitable capacity i.e. in accordance with the capacity of burette to be calibrated and record its weight
  • Clamp the burette under calibration in vertical position and fill it with distilled water, which is in equilibrium with the room temperature, to about 1 cm above the zero line. Note the room temperature and the temperature of water.
  • Open the burette tap to drain out the water slowly to set the base of meniscus accurately against the zero line properly.
  • Place the beaker below the tip of burette. Open the burette tap fully and allow draining the water into tared beaker, until at about 1 cm above the graduation line to be tested. Run the tap slowly and adjust the base of meniscus accurately against the graduation line.
  • Weigh the beaker with water collected; convert the weight of water at room temperature into the volume of water at 27°C by using same equation give above for volumetric flask.
  • Check the results against the tolerances given in the table.

       TOLERANCE ON CAPACITY FOR STANDARD BURETTE

Burette Capacity (ml) 10 25 50 100
Class A Tolerance +/-(ml) 0.01 0.03 0.05 0.1

 

      Calibration of measuring cylinders:

  • Before calibration, clean and dry the measuring cylinders to be calibrated.
  • Weigh the empty measuring cylinder under calibration and record the accurate weight of measuring cylinders.
  • Take distilled water at room temperature and ensure that water attains temperature equilibrium with room temperature by keeping at room temperature for half an hour.
  • Fill the measuring cylinders with distilled water up to the calibration mark, taking care that no water droplets remain on the neck of the measuring cylinders or above the calibration mark.
  • Note the temperature of distilled water used and room temperature.
  • Weigh the filled measuring cylinders and record the weight, subtract the empty weight of measuring cylinders and record the weight.
  • Convert the weight of water at room temperature into volume of water at 27°C by using same equation give above for volumetric flask.
  • Tolerance for capacity is to be confirm from the manufacturers certificate.

       Calibration of graduated pipettes :

  • Before calibration, clean and dry the pipette to be calibrated.
  • Weigh a clean, dry beaker of suitable capacity i.e. in accordance with the capacity of pipette to be calibrated and record its weight.
  • Fill the pipette under calibration by suction of distilled water, having temperature equilibrium with the room temperature, up to the level of 2-3 cm above the graduation line. Note the room temperature and the temperature of water.
  • Wipe the outside of delivery jet of pipette with tissue paper. Hold the pipette in vertical position and allow draining the water until the base of the meniscus is set accurately against the graduation mark.
  • Allow the water to flow down slowly in tared receiving vessel, until graduation line to be tested reaches.
  • Weigh the receiver with water collected in it. Convert the weight of water at room temperature into volume of water at 27°C by using same equation give above for volumetric flask.
  • Check the results against the tolerance given in following table.

     TOLERANCES AND DELIVERY TIMES FOR GRADUATED PIPETTES

Normal Capacity (ml) 2 5 10 20 25
Class A Tolerance +/- (ml) 0.01 0.03 0.05 0.03 0.1

 

 

 

 

 

 

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