Volumetric Measurement in the Laboratory
Volumetric Measurement in the Laboratory
Volumetric measurement is essential in laboratory settings, requiring precise instruments and proper handling. This document provides an overview of volumetric instruments, their classification, and handling, using BRAND laboratory equipment as examples. It is not a substitute for safety instructions or operating manuals.
Standard volumetric instruments include volumetric flasks, bulb pipettes, graduated pipettes, graduated cylinders, and burettes, made from glass or plastic. These instruments are essential for precise liquid measurement, unlike non-calibrated items like beakers and Erlenmeyer flasks.
Two types of glass are used: soda-lime glass for pipettes and borosilicate glass for flasks and cylinders. Calibration is crucial, with instruments calibrated 'to deliver' (TD, Ex) or 'to contain' (TC, In). The standard reference temperature is 20°C. High-quality blanks and controlled heating processes ensure mechanical stability.
Instruments are labeled with nominal capacity, unit symbol, calibration temperature, calibration type, class, waiting time, manufacturer’s name, and material. Class A/AS instruments have the highest accuracy, while Class B instruments have twice the error limits.
Volumetric instruments are classified into Class A/AS/AW and Class B, with Class A/AS/AW offering the highest accuracy. The choice between glass and plastic depends on application needs, with plastic offering high resistance to breakage.
The meniscus, the curvature of a liquid's surface, is crucial for accurate measurement. A concave meniscus requires reading at the lowest point, while a convex meniscus, like with mercury, is read at the highest point. Schellbach stripes improve readability by creating a visual reference.
This document provides essential information on the selection, use, and calibration of volumetric instruments, emphasizing the importance of precision and proper handling in laboratory measurements.
To ensure accurate volume measurements, the meniscus should be read at eye level to avoid parallax errors. A dark background can enhance visibility. Temperature consistency is crucial as liquid expansion can affect volume readings.
For volumetric instruments calibrated to deliver (TD, Ex), the delivery time is the period required for the meniscus to fall from the upper to the lower volume mark. Class AS instruments have a specified waiting time to account for residual liquid flow.
Pipettes are calibrated either 'to deliver' (TD, Ex) or 'to contain' (TC, In). Bulb pipettes generally offer higher accuracy than graduated pipettes. Proper handling involves setting the meniscus accurately and observing waiting times for class AS pipettes.
Volumetric flasks are used for preparing precise dilutions and standard solutions. They are calibrated 'to contain' and require careful filling to the ring mark. Graduated cylinders are also calibrated 'to contain' and are used similarly to volumetric flasks.
Burettes are used for titration and are calibrated 'to deliver'. They require careful handling to avoid overtitration, and the meniscus must be read at eye level. The document outlines the steps for proper burette use and calibration.
Density bottles are used to determine the density of liquids. They are not volumetric instruments but are calibrated 'to contain'. Proper use involves careful temperature control and weighing.
Motorized pipetting aids, such as the accu-jet® pro, offer variable speed control and are used to enhance pipetting accuracy and efficiency. Different delivery modes are used depending on the application, with 'free delivery' preferred for analytical accuracy.
Pipetting aids are essential tools for working with pipettes, offering both motorized and manual options. Motorized aids are suitable for long series pipetting, such as in cell cultures, while manual aids are used for shorter series, primarily in chemical labs. Using pipetting aids reduces the risk of infection or injury compared to mouth pipetting.
To fill a pipette, press the upper button, with the intake rate adjustable by trigger pressure. For delivery, the discharge rate is also adjustable. Options include free delivery or power delivery. It is important not to store the pipette filler in a primed state to prevent liquid uptake.
1. Insert the top of the pipette.
2. Press 'A' and squeeze the ball to create negative pressure.
3. Press 'S' to aspirate liquid above the desired mark.
4. Press 'E' to discharge liquid to the desired mark or drain the pipette.
For viscous media, close the side opening and compress the small ball to blow out.
Manual aids like the macro pipette controller are compatible with a range of pipettes and feature a special valve system for easy meniscus adjustment. They are ideal for small-volume pipettes up to 1 ml, with features like a thumb wheel for liquid intake and delivery, and a large ejector key for pipette ejection.
Modern liquid handling instruments, such as bottletop dispensers and burettes, offer improved precision and ease of operation over traditional volumetric instruments. These instruments are designed for efficient sample preparation and are made from durable materials like ceramic and platinum-iridium.
Bottletop dispensers, available with floating or wiping-seal pistons, are used for precise reagent dispensing. They are suitable for aggressive reagents and organic solvents, with materials chosen based on chemical resistance.
Bottletop burettes allow for precise titration, with direct volume reading from the display. They are suitable for aqueous and non-aqueous solutions, with parts made from resistant materials like borosilicate glass and PTFE.
Air interface pipettes are used for precise liquid handling, with benefits including no instrument wetting and single-use tips to prevent carry-over. Regular calibration is recommended to maintain accuracy.
These pipettes allow simultaneous pipetting operations, ideal for microtiter technology and applications like immunofluorescence and enzyme immunoassays. They are efficient for sample transfer, serial dilutions, and microtiter plate washing.
- Electronic Pipettes: These pipettes use a motor-driven piston controlled by a microprocessor for aspiration and discharge. They offer various pipetting programs such as standard pipetting, dispensing, electrophoresis, reverse pipetting, and mixing of samples.
- Manual Repetitive Pipettes: These devices allow for the dispensing of liquids in a series of equal aliquots without the need for repeated intake. They are robust but can be fatiguing to operate.
- Positive-Displacement Pipettes: Ideal for media with high viscosity or vapor pressure, these pipettes ensure high accuracy and reproducibility by having the piston in direct contact with the liquid.
- Motor-controlled operation reduces physical strain.
- Programs like gel electrophoresis mode and dispensing mode enhance functionality beyond manual pipettes.
- Ergonomic design supports prolonged use without discomfort.
Specifications and Procedures:
All measuring instruments used to confirm product qualities must be monitored. The accuracy and measuring uncertainty of these instruments must be documented before use and tested at defined intervals, as per DIN EN ISO 10 012. The performance of instruments can be affected by factors such as chemical exposure and cleaning frequency, necessitating user-defined testing intervals.
Volumetric instruments are tested gravimetrically, with specific standards applied for different types of instruments (ISO 8655 for liquid handling, ISO 4787 for glass volumetric). BRAND provides Standard Operating Procedures (SOPs) and software to facilitate testing, ensuring quick and inexpensive procedures.
Calibration involves determining the actual volume delivered, while adjustment corrects deviations from the nominal value. Detailed instructions are provided by BRAND, and adjustments typically involve turning an adjustment screw followed by recalibration.
Instruments marked to "MessEV" are subject to monitoring, though initial testing is not clearly mandated. It is recommended to test a representative sample to document the initial state.
EASYCAL™ software aids in monitoring to GLP and DIN EN ISO 9001 standards, automating calculations and documentation. It supports manual entry or direct import from balances, with results stored in a database.
The IVD Directive defines in-vitro diagnostic medical devices and their regulatory requirements. The CE mark indicates compliance with European safety and environmental standards.
Various certificates, such as quality certificates, declarations of conformity, and DAkkS Calibration Certificates, ensure compliance with standards and traceability of measurement results.
The document outlines specifications for laboratory instruments, including manufacturer details, product and batch numbers, measurement values, and error limits. Certificates are provided for both batch and individual instruments, ensuring conformity and quality.
Certificates include product designation, issue date, manufacturer, laws and technical rules, and accreditation details. Instruments like BLAUBRAND® volumetric instruments and various liquid handling tools come with standard certificates. Standards such as ISO and USP are crucial for ensuring reliable results, with specific regulations for European and American markets.
BRAND's quality management system, certified to DIN EN ISO 9001, involves process monitoring and random checks to ensure high accuracy and minimal deviation in volumetric instruments. All test results are documented and traceable for seven years.
Labware cleaning methods include manual, machine, and ultrasonic cleaning. Immediate cleaning at low temperatures with low alkaline detergents is recommended to prevent damage. Specific guidelines are provided for cleaning glass and plastic labware.
Instruments in contact with infectious materials must be disinfected and possibly sterilized. Steam sterilization is detailed, with precautions for different materials. Thermal resistance guidelines are provided for BLAUBRAND® and SILBERBRAND instruments.
Handling hazardous substances requires adherence to regulations for personal and environmental safety. Instruments must be checked for suitability and functionality before use. Safety precautions include avoiding sudden temperature changes and ensuring proper disposal of waste.
Catalog excerpts
Volumetric Measurement in the Laboratory Learning the basics – how to work with volumetric instruments.
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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'...
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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
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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 only...
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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 producing...
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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 legibility....
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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 Calibration:...
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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 higher...
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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 diameter...
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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 the...
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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 AS:...
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