Volume Measurement and Calibration
Volume Measurement in Industrial and Analytical Operations
• Crucial in fields like chemistry, health, biology, pharmacy, and fuel depot.
• Reliable and accurate volume quantities measured using volume instruments are essential.
• Calibration of volume instruments using correct methods is necessary to reduce errors in liquid handling.
Volume Instrument Calibration Methods
• Volume instruments can be calibrated by filling or emptying using a reference volume measurement, comparing two volumes (volumetric method), or by weighing the quantity of a suitable liquid, contained or delivered by the volume instrument.
• Weighing is the most important step in gravimetric calibration, influenced by factors such as the resolution and sensitivity of the balance, calibration of the balance, and the class and density of the reference weights used to calibrate an electronic scale or balance.
Ambient Conditions and Calibration
• Ambient conditions such as air temperature, humidity, and barometric pressure influence gravimetric measurement mainly through air density determination.
• Calibration must be carried out after the temperature between the calibration object and the environment has been equalized, with an equalization time of at least 2 hours observed for starting calibration.
Volumetric Method
• Applies to calibrating any size of volume measures for which standard pipets of comparable volume are available.
• The precision of calibration depends on the care exercised in adjusting the various volumes and strict adherence to the procedure.
Calibration of Flask
• Involves an initial wet-down using the correct drain procedure, then nearly filled with water delivered from a calibrated pipet.
• Additional water is added until the meniscus in the test item coincides with the calibration graduation mark.
Standards and Equipment for Calibration
• Standard and equipment for calibrating volume instruments include calibrated standard volume measures, calibrated burette(s), calibrated thermometers, meniscus reading device, and stopwatch or other suitable timing device.
Uncertainties of Measurement
• The Calibration guide 03 G-CAL-003 outlines the standard uncertainty of measurement for volume measuring instruments.
• Uncertainties include mass of delivered/contained water, water temperature/water density, air density, air temperature, air pressure, relative air humidity, temperature of the volumetric instrument for glassware and standard measuring cans, thermal expansion coefficient, standard deviation or repeated measurements, meniscus reading only for glassware and standard measuring cans, process-related handling influences only for piston pipettes, and systematic influences due to the air cushion only for piston pipettes.
