Volumetric Instruments in the Laboratory Types, Applications, Certifications and Standards

Volume measurement is one of the fundamental tasks in the laboratory, and a wide range of different volumetric instruments from BRAND are available for this purpose. On this page, you will find a compact overview of the most important types of instruments, typical applications, as well as key aspects relating to certificates, standards and handling, based on BRAND’s more than 75 years of experience in the field of volumetric instruments.

Volumetric instruments in the laboratory (whether in chemistry or biology) are special measuring instruments used to measure, dispense or transfer liquids as accurately as possible. They are classified as inspection and measuring equipment, i.e. instruments that make it possible to reliably verify agreed characteristics (e.g. concentration, content, titer) in the first place. They are primarily used for preparing analyses of liquids and for the actual analysis itself.

It is important to note that in the laboratory, volume is often not merely an “auxiliary quantity”, but part of the measured value (e.g. in titration). For this reason, volumetric instruments differ fundamentally from measuring cups or household measuring vessels: they are designed according to standards, error limits, type of adjustment (In/Ex) and a reference temperature, and they must be regularly monitored and calibrated, particularly in regulated environments.

Several basic types have become established in the laboratory. They differ primarily in whether they provide a fixed target volume or allow variable partial volumes, how they are adjusted, and how strongly the result depends on reading and handling (meniscus, delivery/waiting time, wetting).

The most important types of volumetric instruments made of glass or plastic are:

In addition to the volumetric instruments made of glass or plastic described here, liquid handling instruments according to DIN EN ISO 8655 (e.g. Dispensette®, Transferpette® or HandyStep®) are also classified as volumetric instruments. These use a piston and therefore have a different operating principle than volumetric instruments made of glass or plastic.

Volumetric instruments are needed whenever a volume has to be set precisely or used as a measured quantity. This is the case wherever analytical results such as concentrations or dilution factors are derived directly from volume. A simple classification helps with the selection: sample preparation (volume as a reference) vs. analysis (volume as part of the measured value).

Volumetric instruments differ primarily in terms of volume type (fixed vs. variable), adjustment (In vs. Ex or TC vs. TD), accuracy class (A vs. B), and material (glass vs. plastic).

The 4 most important distinctions between volumetric instruments are:

1. Fixed vs. variable volume

• Fixed volume: A single ring mark indicates the nominal volume for the reproducible preparation or transfer of a fixed volume. The design combines a large body for the main portion of the volume with a slender, cylindrical neck with a small diameter (e.g. volumetric flasks and volumetric pipettes).
• Variable volume: A continuous scale allows different partial volumes to be set and read. The cylindrical body with a larger cross-section represents the respective error limit at each individual volume over the entire scale range (e.g. burettes, graduated pipettes, graduated/mixing cylinders).

2. In vs. Ex oder TC vs. TD

• In: The instrument is manufactured so that it contains the nominal volume. When pouring out, a residual amount of liquid always remains.
• Ex: The instrument is manufactured so that it delivers the nominal volume. After delivery, a defined residual amount may remain in the instrument. A specified waiting time may be part of the specification and must be observed.

3. Class A vs. Class B

• Class A (AS/AW): Refers to the highest accuracy class, i.e. the smallest error limits. Volumetric instruments of this class are therefore suitable when low measurement uncertainties are required (e.g. for calibration work, analytical applications). Wide-neck volumetric flasks have a neck with a slightly larger cross-section and are designated as Class AW, as they therefore also have a slightly higher error limit compared to Class A volumetric flasks. Class AS volumetric instruments are always adjusted to Ex. The suffix “S” means fast delivery.
• Class B: The tolerances are larger than for Class A and are therefore intended for preparatory work where speed, robustness or cost are the main priorities. Here, too, there are wide-neck volumetric flasks which, due to the larger cross-section and the associated increased error limit, are designated as BW.

4. Glass vs. Plastic

• Glass (for volumetric instruments, generally borosilicate glass or soda-lime glass): Very dimensionally stable and therefore has low thermal expansion. It is transparent and offers high chemical resistance to acids, alkalis or aqueous solutions, with the exception of hydrofluoric acid (HF). Volumetric instruments made of glass change their volume only very slowly, particularly as a result of cleaning.
• Plastic (e.g. PP, PMP, PS): Is necessary when glass is unsuitable (e.g. for HF or in trace analysis depending on the element/matrix, boron, aluminium), but has different limitations in terms of chemical and temperature resistance compared to glass. Plastic is characterized by high break resistance and lower weight. PMP and PFA are also used for measuring instruments that comply with Class A error limits.

The following key points are important when handling volumetric instruments:

1.    Read the meniscus correctly

       When read correctly, volumetric instruments made of glass are the most accurate measuring instruments for volumes in the laboratory. 

       Find out here how to read the meniscus correctly.

2. Correct handling

   Requirements regarding waiting times, angle and wiping affect the precise volume and must be observed depending on the instrument.

   More information on handling the individual volumetric instruments.

3. Observe the reference temperature

   The specified volume refers to the reference temperature indicated on the volumetric instrument (typically 20 °C), at which the instrument was calibrated. For the most accurate measurement results, the same temperature should be maintained whenever possible. In the case of significant deviations from the reference temperature, temperature-related volume changes must be taken into account in calculations. 

4.    Ensure cleanliness and wetting

       Residues, e.g. grease films or limescale deposits (powder), interfere with wetting and distort the meniscus. 

       Clean, rinse and dry before use. 

       Find out more about the correct cleaning of laboratory equipment here.

5.   Inspection and calibration status

      A visual inspection should be carried out before each use (e.g. cracks, chipped edges, damaged scale).

      In addition, regular recurring calibrations should be carried out in accordance with measuring equipment monitoring. 

A basic distinction is made between quality certificates (batch and individual certificates), declarations of conformity and calibration certificates. All certificates document traceability, with the level of documentation increasing from the batch certificate to the individual certificate and finally to the DAkkS calibration certificate. In addition, the DE-M marking indicates conformity with the German Measuring Instruments Ordinance.

Volumetric instruments are subject to a general basic standard, specific product standards for each type of instrument, and a central testing standard for calibration and application:

Details for comparison: G.I.T. Laboratory Journal 9–10 / 2013, pp. 33–35

Jander Jahr Maßanalyse (17. Auflage)

G.I.T. Laboratory Journal 9-10 / 2013, pp 33-35