Calibration of Volumetric Glassware By Gravimetric Method Nihal Gunasekara Sri Lanka Bangladesh BEST Programme

Laboratory used Glassware  Burette  Single-volume pipette  Graduated pipettes  One-mark volumetric flasks  Graduated measuring cylinders Bangladesh BEST Programme

DEFINITIONS  Unit of volume Cubic centimeter : ml  Ref. temperature 20 °C  To deliver Apparatus is calibrated to accurately transfer the stated volume to another container.  To contain Apparatus is calibrated to an accurate measure of the volume contained Bangladesh BEST Programme

Apparatus Needed  Balance  Thermometer  Hygrometer  Barometer  Water Distilled water /De-ironized  Pipette Sucker Bangladesh BEST Programme

Recommended Apparatus - Balance Selected Volume (V)Resolution of Balance (mg) Std. Deviation (mg) 10 ml < V < 1000 ml ml < V < 2000 ml V > 2000 ml Bangladesh BEST Programme

Recommended Apparatus/Liquids Apparatus/Liquid Maximum Error Thermometer 0.1 °C Hygrometer 5% Barometer 1 k Pa Calibration Liquid Distilled /de-ionized water Bangladesh BEST Programme

Test Room Conditions Temperature Maintained at 20 ± 1 °C and during calibration ± 0. 5 °C stability Humidity Maintained 35% to 85% Prefer to maintain at 60 ± 10% Stabilization Volumetric instruments and test water 1 to 2 hours M Bangladesh BEST Programme

Preparation Cleaning of volumetric glassware  Internal surface of volumetric vessels shall be cleaned sufficiently before the calibration  Oil or grease is removed by suitable solvent  The vessel should be nearly filled with an aqueous solution of a soap less detergent and shaken vigorously. It should then be repeatedly rinsed with distilled water  Be sure that vessel is cleaned before commence calibration Bangladesh BEST Programme

Calibration Procedure  Prior to any calibration test make sure that all instruments reached the ambient temperature in the laboratory  During the calibration maximum temperature variation in the laboratory should not exceed ±0.5 o C.  Set or read a meniscus against a reference line or scale  Be sure that the vessel or weighing bottle and the distilled water are at room temperature. Bangladesh BEST Programme

Calibration Procedure  Fill distilled water up to the required volume  Weigh the testing container with distilled water.  Measure the temperature of distilled water using the thermometer.  Repeat the above step three times and record in the data recording form.  Repeat the above steps for cylinders at least at four different volumes Bangladesh BEST Programme

Calibration Procedure –Flask & Cylinder (contain) 1.Weigh the empty testing container and record the value 2.Fill distilled water up to the required volume 3.Weigh the testing container with distilled water. 4.Measure the temperature of distilled water using the thermometer. 5.Repeat the above step 2 through 4 three times and record in the data recording form. 6.Repeat the above step 2 through 5 for cylinders at least at three different volumes Bangladesh BEST Programme

Calibration Procedure – Pipette (deliver) 1.Weigh a empty container and record the value 2.Fill pipette with distilled water up to the index mark 3.Any water on the outside of the tip is removed with filter paper after the filling is completed 4.Transfer the distilled water to empty vessel, weighted in step (1) 5.Weigh the vessel with distilled water. 6.Measure temperature of distilled water using the thermometer 7.Repeat the above steps three times and record in the data recording form. Bangladesh BEST Programme

Calibration Procedure – Burette (deliver) 1.Weigh empty container and record the value 2.Fill burettes with distilled water up to the index mark 3.Any water on the outside of the tip is removed with filter paper after the filling is completed 4.Transfer the distilled water to empty vessel, weighed in step (1) 5.Weigh the vessel with distilled water 6.Measure temperature of distilled water using the thermometer. 7.Repeat the above steps three times and record in the data recording form. 8.Repeat the above steps 1 through 7 for Burettes at least three different levels Bangladesh BEST Programme

14 Principle of calibration - volumetric glass ware Bouncy effect Temperature effect Bangladesh BEST Programme Z values are given in Tables B6, B7 and B8 in ISO 4787 : 2010 for different types of glass at common air pressure Vs temperature

Notations R L- is the balance reading of vessel with water reference liquid in grams R E - is the balance reading of empty vessel in grams Ρ a - is the density of air, in grams per milliliter ρ b - when weighing in air as though the density of the weight was 8.0 g/ml. ρ w - is the density of water at t o C, in grams per milliliter. ϒ - is the coefficient of cubical thermal expansion of the material of which the item of glassware, tested is made in reciprocal degrees Celsius, t - is the temperature of the water used in testing in degrees Celsius. Bangladesh BEST Programme

Density of Air- Table B3 ISO 4787 Temperature Air Pressure hPa Density values in 10 grams per milliliter Bangladesh BEST Programme -3

Density of water – Table B4 ISO 4787 Temperature Density (g/ml) °C ρ w Bangladesh BEST Programme

Coefficient of Cubical Thermal Expansion Material Coefficient of cubical thermal expansion ϒ -1 °C Borosilicate glass Borosilicate glass Soda-lime glass 27 Bangladesh BEST Programme

Data Recording  Use spread sheet for data recording  Record Temperature, Humidity, Barometric pressure  Record final data in a data recording sheet  Review from a third party  Prepare the final calibration certificate Bangladesh BEST Programme

20 Bangladesh BEST Programme