Calibration of Volumetric Glassware

Wash, clean and dry glassware thoroughly. Ensure that a satisfactory method of cleaning is employed, since any contamination will effect the meniscus shape/level.

During calibration it is critical that all internal surfaces are clean and dry to avoid moisture droplets or contaminats.

Delivery glassware should be timed before calibration to ensure that total delivery time is within tolerances specified by the relevant British and ISO standards.

With delivery glassware such as pipettes and burettes, weigh and tare a suitable sized weighing vessel.

Balances should accurately read to five decimal places. Glassware should be maintained at a controlled room temperature (air conditioning).

Fill with purified water a few millimeters above the graduation line. Pipettes and burettes should be filled from below, i.e. through the tip. If burettes are filled from the top for added convenience, take care to avoid wetting the walls above the upper graduation line and check that no air is entrapped in the stopcock.

For pipettes and burettes control the flow of excess liquid from the tip to allow the meniscus to settle exactly on the calibration line. For flasks and cylinders remove excess water to match meniscus and calibration line exactly using a pipette and bulb.

When setting the meniscus ensure that the glassware is vertical. Ensure parallax error is avoided by viewing the meniscus from a level height against a white background.

A black shade should be secured either around the article to be tested or placed behind it. The shade should be below the setting height (approx 1 mm lower). Ensure the meniscus edge is smooth, straight and level.

For graduated/bulb pipettes and burettes, dispense water into tared weighing vessel and weigh. For flasks and cylinders weigh the tared and filled glassware. Record the result from the balance. Use a certified Class A thermometer to measure the water temperature. Add the water temperature correction figure from Table 1 or 2 to the net weight obtained.

Measure the barometer reading and air temperature and add (or substract if minus) the correction figure from Table 3.

This produces the final gravimetric result which has already been converted to the volumetric figure in millilitres. All of the procedure described must be followed to ensure that consistently accurate results are obtained.