A serological pipette is a fundamental piece of laboratory equipment used for the precise measurement and transfer of liquid volumes within scientific settings. This graduated tool is a mainstay in biology, chemistry, and clinical laboratories due to its accuracy across a broad range of volumes. The instrument significantly advanced biomedical sciences, particularly in fields like serology and microbiology, where accurate liquid handling is necessary for reliable results. It remains an indispensable device for researchers needing to move specific quantities of solution in a controlled manner.
Anatomy and Mechanism of Operation
The serological pipette is characterized by its long, slender tube that tapers to a narrow opening at the dispensing end. Clear markings along its length allow a user to gauge the volume of liquid being drawn up or expelled. The opposite end is the aspiration end, designed to connect securely to an external suction device.
A small, porous filter plug is located near the top of the pipette for contamination control. This plug prevents aerosols and excess liquid from being accidentally drawn into the mechanical pipette aid. The pipette relies entirely on a separate pump or controller to create suction.
A pipette aid is attached to the aspiration end and utilizes a motorized or manual piston to create a vacuum. When activated, the vacuum draws the liquid up through the tip and into the calibrated tube. Releasing the vacuum allows the measured volume to flow out precisely.
Essential Features and Standardized Markings
Serological pipettes are manufactured from two primary materials: reusable glass or transparent, single-use plastic. Plastic is most common for disposable applications and significantly reduces the risk of cross-contamination. All pipettes feature printed graduations along their length to indicate the volume.
This measurement is known as ‘TD’ or “To Deliver” accuracy, meaning the volume indicated is the volume that exits the pipette when used correctly. Volume markings often feature both standard and reverse graduation. Standard graduation begins with zero at the top and increases toward the tip, allowing the user to measure the volume dispensed.
Reverse or “negative” graduation marks extend the scale above the maximum stated volume. This provides a small amount of extra capacity for applications requiring slight over-aspiration.
A standardized color-coding system is applied to the aspiration end for quick identification of the maximum volume. For example, a yellow ring might signify a 5 mL pipette, while a blue ring indicates a 10 mL size. Serological pipettes, with their multiple graduation marks, are distinct from volumetric pipettes, which measure only one fixed volume with the highest precision.
Primary Uses in Biological Science
Serological pipettes are primarily used for transferring medium to large volumes, typically ranging from 1 milliliter up to 50 milliliters. They are frequently used for preparing large batches of solutions, such as mixing buffers, stock solutions, and chemical reagents.
A major application is in cell culture laboratories, where the pipettes are used to aseptically transfer media, add supplements, or gently mix cell suspensions. They also facilitate the sequential transfer of liquid during quantitative assays like serial dilution. Serological pipettes are also employed to carefully layer liquids of different densities, such as when preparing a density gradient for sample purification.