The term “aliquot” refers to a precise portion of a larger total volume of a sample, typically a liquid solution, which is separated for analysis or storage. In chemistry, biology, and clinical laboratory settings, dividing a main sample into smaller, identical parts is a fundamental technique for managing resources and maintaining sample quality. This practice helps researchers work with manageable amounts of material while obtaining reliable and reproducible scientific data.
Defining the Aliquot
An aliquot is a fraction of a solution or suspension taken from a bulk source for a specific purpose, such as testing or long-term archiving. The defining characteristic of an aliquot is that it must be homogeneous, meaning its chemical composition and properties are identical to the original parent sample. Although the aliquot is smaller in quantity, it remains a true and representative mirror of the entire volume.
The action of creating these smaller portions is referred to as “aliquoting,” and it is performed by precisely measuring a volume from the main stock. These portions are typically small, often in the microliter or milliliter range, with the exact size dictated by the requirements of the experiment. This intentional division ensures that a limited, valuable sample can be distributed across multiple applications.
The Purpose of Aliquoting in Laboratory Work
Aliquoting is a cornerstone of good laboratory practice. One primary benefit is minimizing contamination risk to the original sample. By limiting how often the primary stock container is opened and accessed, the chance of introducing external microbes or chemical impurities is greatly reduced.
For many biological samples, such as serum, plasma, proteins, or DNA, repeated freeze-thaw cycles cause significant degradation of heat-sensitive components. Each cycle can damage molecular structure or reduce the activity of biomolecules, making subsequent measurements inaccurate. Aliquoting allows researchers to thaw only the small portion needed for a single experiment, leaving the remaining stock frozen and intact for future work.
Creating multiple, standardized aliquots facilitates accurate and consistent measurement across numerous trials. When the starting material for every test is a precisely measured and representative portion, it enables standardized testing and enhances the reproducibility of results. This standardization is particularly important in clinical and pharmaceutical research where accuracy is paramount for patient care and regulatory compliance.
Essential Techniques and Equipment
The successful creation of aliquots relies on accurate measuring devices and sterile technique. Micropipettes and volumetric pipettes are the standard tools employed to transfer precise volumes, ensuring each aliquot contains the intended amount of material. These instruments must be regularly calibrated to prevent systematic errors in volume transfer that could skew experimental outcomes.
Aseptic technique is necessary during the transfer process to prevent cross-contamination or the introduction of environmental contaminants. The aliquots are typically dispensed into specialized containers, such as polypropylene cryovials, which are designed to withstand ultra-low storage temperatures, often down to -80°C or in liquid nitrogen. Proper labeling of each cryovial is mandatory, requiring specific details like the parent sample identification, volume, and date of aliquoting to ensure traceability.
Aliquot Versus Related Concepts
While the term aliquot describes a portion of a larger whole, it is distinct from other related laboratory terms like dilution and sub-sample. A dilution is a process that specifically reduces the concentration of a solute in a solution, usually by adding a solvent or diluent. An aliquot, however, is simply a measured portion of the original concentration, which may or may not be used as the starting volume for a dilution series.
The term sub-sample is a broader concept that can describe any smaller portion taken from a larger sample, which might not be precisely measured or homogeneous. In contrast, an aliquot is defined by its precision; it is a quantified fraction expressly intended to be a representative and exact division of the parent material. This emphasis on accuracy makes the aliquot a more specific and controlled form of sub-sampling used in quantitative analysis.