Volumetric Measurement in the Laboratory

Learning the basics – how to work with volumetric instruments. Volumetric Measurement in the Laboratory FIRST CLASS·BRAND 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 Measurement' is designed to give the reader a quick overview of volumetric instruments. It is not intended to replace the operating manuals of the liquid handling instruments described. By all means, read the operating manuals supplied with these instruments before use – for your own safety and success. Please do not hesitate to contact us if you have any further questions on the subject of volumetric measurement. BRAND GMBH + CO KG P.O. Box 11 55 97861 Wertheim/Main · Germany Telephone: +49 9342 808-0 Fax: +49 9342 808-98000 E-Mail: [email protected] Internet: www.brand.de © BRAND GMBH + CO KG · All rights reserved Contents n Volumetric Instruments – an Overview 5 n Manufacture of Glass Volumetric Instruments 6 From raw material to finished precision instrument 6 Identification of volumetric instruments 8 Accuracy classification of volumetric instruments 9 n Working with Volumetric Instruments 10 Meniscus of a liquid 10 Delivery and waiting times 11 Pipettes, general 12 Handling of pipettes 13 Handling of volumetric flasks 15 Handling of graduated and mixing cylinders 15 Handling of burettes 16 Handling of density bottles 17 Working with pipetting aids 18 n Working with Liquid Handling Instruments 21 Dispensing with bottletop dispensers 22 Titrating with bottletop burettes 24 Pipetting with air-interface pipettes 25 Pipetting with positive-displacement pipettes 29 Dispensing with repetitive pipettes 30 n Accuracy Defined 32 n Monitoring of Measuring Instruments 33 Procedure for volumetric testing 34 Calibration software 36 Calibration service 36 n Conformity and Calibration Certificates 37 ® n BLAUBRAND USP volumetric instruments 38 n IVD Directive 39 n Quality Management 40 n Cleaning of Laboratory Equipment 41 n Safety Information 43 Volumetric Instruments – an Overview Volumetric Instruments – an Overview The volumetric measurement of liquids is a routine operation in the laboratory. Therefore, Volumetric instruments volumetric instruments, such as volumetric flasks, bulb pipettes, graduated pipettes, graduated glass/plastics cylinders and burettes are standard equipment. They can be made from glass or plastic. Sup- pliers 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 only as an approximate guide. A selection of volumetric instruments by BRAND is illustrated below: Volumetric flasks Bulb pipette Graduated pipette Graduated cylinder Burette Liquid handling instruments To meet the ever growing demands on volumetric measuring in the lab, such as testing in series, new devices are constantly being developed, e.g., for dispensing, pipetting and titrating. Usually, the instruments designed by different manufacturers for a particular purpose are more or less similar in functional principle. However, major differences are apparent when the focus is on constructional details and design. This selection of liquid handling instruments by BRAND illustrates the range of instruments avail- able: Bottletop dispenser Bottletop dispenser Bottletop burette Single-channel Multichannel Positive displace- Repetitive pipette, Repetitive pipette, air interface pipettes air interface pipettes ment pipette manual electronic BRAND 5 Glass Volumetric Instruments · Manufacture Manufacture of Glass Volumetric Instruments From raw material to finished precision instrument Blanks The glass types used are soda- This results in optimum me- sterilizer without any resulting Therefore: lime glass (e.g., AR-GLAS®) chanical stability, a requirement volume changes. Always place glass instruments for bulb and graduated pi- for keeping the volume con- As with all glass instruments, into a cold drying cabinet or pettes, and borosilicate glass stant despite any subsequent however it should be noted, sterilizer; then heat slowly. At (e.g., Borosilicate glass 3.3) temperature fluctuations. that uneven heating or sudden the end of the drying or steril- for volumetric flasks, graduated Therefore, BLAUBRAND® and temperature changes produce izing period, allow instruments cylinders and burettes. These SILBERBRAND volumetric thermal stresses, which may to cool off slowly inside the glass types meet instruments can be heated up result in breakage. switched-off drying cabinet or the stringent laboratory re- to 250 °C in a drying cabinet or sterilizer. Never heat volumetric quirements for chemical and instruments on a hotplate! physical resilience. High-quality blanks and strict statistical testing of the required quality characteristics are the basis for producing high-quality volumetric instruments. For example, thermal stress in the glass blanks must be eliminated by a controlled heating and cooling process. Blanks for graduated cylinders Calibration Every glass volumetric instru- Volumetric instruments are either calibrated 'to contain' ('In') ment is individually calibrated at or 'to deliver' ('Ex'). BRAND, i.e. the instrument is accurately filled with a defined Calibration 'to contain' Calibration 'to deliver' Reference temperature quantity of water, and a calibra- (TC, In): (TD, Ex): The standard reference tem- tion mark is applied at the low- The contained quantity of liquid The delivered quantity of liquid perature, i.e. the temperature est point of the meniscus. In corresponds to the capacity corresponds to the capacity at which volumetric instruments the case of graduated instru- printed on the instrument. printed on the instrument. will contain or dispense their ments, two calibration marks These instruments include e.g., The wetting residue remaining volumes, is 20 °C. are applied. graduated cylinders, volumetric in the instrument has already If the adjustment or calibra- Computer-controlled systems flasks, and capillary pipettes up been taken into account in the tion is performed at a temper- ensure maximum precision in a to 200 µl. calibration. These instruments ature that deviates from this fully automated production line. include e.g., graduated and standard, the corresponding 'Statistical Process Control' bulb pipettes, and burettes. measurement values must be (SPC) guarantees production of corrected. volumetric instruments with the smallest deviation from nominal Note: capacity (accuracy) and narrow Due to the small coefficient of scatter of individual values expansion of the glass material, (coefficient of variation). the reference temperature is of minor significance in practical use since the measurement de- viations resulting from volume expansion of the measuring instrument are generally smaller than the error limit. Calibration of graduated pipettes BRAND 6 Glass Volumetric Instruments · Manufacture Silk-screening Screening inks Calibration is followed by BRAND uses quality inks manufactured especially for glass volumetric instruments: silk-screen printing of marks and inscriptions. BRAND uses stretchable screen stencils for Blue enamel: White enamel: Amber diffusion stain: all graduated pipettes, burettes, High contrast, optimum White enamel is used for Diffuses into the glass sur- graduated cylinders, and mix- combination of resistance and SILBERBRAND volumetric face and can only be removed ing cylinders. These stencils legibility. Blue enamel is used instruments (class B). by abrasion. It is used for can be stretched to match the for BLAUBRAND® volumetric volumetric instruments that are calibration marks accurately, so instruments (class A/AS). exposed to especially aggres- that the measuring precision is sive cleaning conditions. An maintained for all intermediate amber diffusion dye is used volumes. for BLAUBRAND® ETERNA volumetric instruments (class Pipettes are additionally marked A/AS) as well as for SILBER- with 'color-code' rings at their BRAND ETERNA volumetric upper end, which make it easier instruments (class B). to identify similar pipette sizes clearly. The ISO 1769 industry standard defines color-coding for different nominal volumes. Automatic silk-screening of volumetric flasks Firing Quality assurance Firing or annealing the Quality assurance is imple- screened ink is the last step on mented at BRAND through the way from the blank to the ongoing testing during produc- finished volumetric instrument. tion and statistical testing in the A carefully controlled anneal- final inspection. (For detailed ing process, along with the information, see page 39.) specially produced quality inks, is a prerequisite for durable graduations. This involves a gradual heating and cooling of the volumetric instruments. De- pending on the type of glass, temperatures of 400 to 550 °C are reached in this process. Silk-screened graduated cylinders before firing BRAND 7 Glass Volumetric Instruments · Manufacture Identification of volumetric instruments Batch number Example: BLAUBRAND®

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