Volumetric Measurement in the Laboratory
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Volumetric Measurement in the Laboratory Learning the basics – how to work with volumetric instruments.

Introduction Volumetric measurement plays a central role in the laboratory. The user has to determine the degree of accuracy required for each measurement. Based on this, he can choose the appropriate volumetric instrument. Reliable measurements require the use of precision instruments and their proper handling. To provide a better understanding of volumetric instruments and their operation, this booklet explains the most important terms for their classification and handling, and illustrates them by using BRAND laboratory equipment as examples. The brochure 'Information on Volumetric...

Identification of volumetric instruments Accuracy classification of volumetric instruments Handling of volumetric flasks Handling of graduated and mixing cylinders Handling of density bottles Working with pipetting aids Titrating with bottletop burettes Pipetting with air-interface pipettes Pipetting with positive-displacement pipettes Dispensing with repetitive pipettes Calibration software Calibration service

Volumetric Instruments Volumetric Instruments – an Overview Volumetric instruments glass/plastics The volumetric measurement of liquids is a routine operation in the laboratory. Therefore, volumetric instruments, such as volumetric flasks, bulb pipettes, graduated pipettes, graduated cylinders and burettes are standard equipment. They can be made from glass or plastic. Suppliers offer volumetric instruments in varying qualities. Graduated beakers, beakers, Erlenmeyer flasks, dropping funnels and the like are not volumetric instruments! They are not precisely calibrated, and the scale serves...

Glass Volumetric Instruments · Manufacture Manufacture of Glass Volumetric Instruments From raw material to finished precision instrument Blanks Two types of glass are used for the production of blanks: – soda-lime glass (e.g., AR-GLAS®) for bulb and graduated pipettes – borosilicate glass (typically Borosilicate glass 3.3) for volumetric flasks, graduated cylinders and burettes. These glass types meet the stringent laboratory requirements for chemical and physical resilience. High-quality blanks and strict statistical testing of the required quality characteristics are the basis for...

Glass Volumetric Instruments · Manufacture Screening inks Calibration is followed by silk-screen printing of marks and inscriptions. BRAND uses stretchable screen stencils for all graduated pipettes, burettes, graduated cylinders, and mixing cylinders. These stencils can be stretched to match the calibration marks accurately, so that the measuring precision is maintained for all intermediate volumes. BRAND uses quality inks manufactured especially for glass volumetric instruments: Blue enamel: White enamel: Amber diffusion stain: High contrast, optimum combination of resistance and...

Glass Volumetric Instruments · Manufacture Identification of volumetric instruments Batch 03 with year identification DE-M 19 Example: BLAUBRAND® bulb pipette Manufacturer Designation of the standard BRAND trademark for volumetric instruments class A/AS Country of origin Reference temperature (20 °C), waiting time (5 sec.), calibration (TD, Ex = to deliver) Nominal volume Error limit Class 'A', the highest quality grade, 'S' for swift delivery Volume unit The labeling below must be printed on every volumetric instrument: Error limit Manufacurer's trademark (here: BLAUBRAND®) Batch number n...

Glass Volumetric Instruments · Manufacture Accuracy classification Volumetric instruments are generally available in two accuracy classes: Class A/AS/AW Volumetric instruments of class A and AS have identical error limits as established by DIN EN ISO. These are generally implemented only in glass volumetric instruments. Exceptions are BRAND plastic volumetric flasks made from PFA and PMP and plastic graduated cylinders made from PMP, which are designed to meet the highest requirements and likewise correspond to class A. Measuring flasks with wide neck are marked with class AW and have a...

Volumetric Instruments of Glass · Measuring the Volume Working with Volumetric Instruments The liquid meniscus The term meniscus describes a curvature in the surface of the liquid. The meniscus may be curving upwards or downwards. The curvature develops as a function of the interplay between the adhesion and cohesion forces. If the liquid molecules are attracted more strongly by the glass wall (adhesion) than by their own kind (cohesion), the meniscus is curved downwards, or concave; the edge of the liquid surface is slightly raised. This is the case, e.g., with aqueous solutions. If the...

Volumetric Instruments of Glass · Measuring the Volume Delivery and waiting times In volumetric instruments for liquid delivery (calibrated to deliver, TD, Ex), the volume delivered is always smaller than the volume contained in the measuring instrument. This is caused by the fact that a certain amount of liquid remains as a film on the inner surface of the instrument. The volume of this liquid film depends on the delivery time and should be taken into account when calibrating the measuring instrument. Possible volume errors: The volume delivered from a pipette or burette becomes smaller if...

Glass Volumetric Instruments · Handling Working with Volumetric Instruments Pipettes, general Pipettes are volumetric instruments for measuring volumes of liquid and are generally calibrated 'to deliver'. During the manufacturing process, they are individually volumetrically calibrated and provided with one or more calibration marks. We distinguish between bulb and graduated pipettes (calibrated to deliver, TD, Ex) and disposable micropipettes up to 200 µl (calibrated to contain, TC, In). Bulb pipettes Graduated pipettes ■ Calibration: Class AS: 'Ex + 5 s' Class B: 'Ex' ■ Calibration: Class...

Glass Volumetric Instruments · Handling Handling of pipettes Pipettes calibrated 'to deliver' ('TD, Ex') Proper pipetting with bulb pipettes with 1 mark (here: nominal volume 25 ml) and graduated pipettes type 2, class AS (here: partial volume 3 ml) Utility: pipetting aid (see page 18) Filling 1. Fill the pipette with a pipetting aid to approx. 5 mm above the selected graduation mark. 2. Remove any liquid remaining on the outside of the tip of the pipette with a tissue. total delivery, partial delivery, total delivery, Bulb pipette 1 mark 3. Set the meniscus. 4. Wipe off any drop of liquid...