A conical tube is a fundamental piece of disposable plastic laboratory equipment designed for the handling and processing of liquid samples in scientific and medical settings. The tube’s defining characteristic is its tapered bottom, which plays a specific role in sample manipulation. These vessels are ubiquitous across numerous disciplines, providing a standardized, sterile environment for a wide range of laboratory procedures.
Physical Structure and Materials
The physical design of the conical tube is highly optimized for laboratory work, consisting of a cylindrical body that narrows into a distinct cone shape at the bottom. This structure is topped with a secure, leak-proof screw-cap, which prevents leakage, especially when the tube is subjected to rapid movement.
The vast majority of conical tubes are manufactured from polypropylene, a type of plastic chosen for its robust chemical resistance and durability. This material also tolerates a wide range of temperatures, making the tubes suitable for both room-temperature processes and long-term freezing, often down to -80°C.
Volume markings, known as graduations, are molded or printed along the side of the tube body to allow researchers to quickly estimate the liquid volume inside. The tubes are routinely sterilized during manufacturing to ensure they are free of biological contaminants like nucleases, endotoxins, and pyrogens. This sterility is a requirement for sensitive biological applications, such as cell culture and molecular biology assays.
Why the Cone Matters: Centrifugation
The primary function and defining purpose of the conical tube revolve around the process of centrifugation. Centrifugation is a technique that uses centrifugal force generated by spinning to separate components of a mixture based on their density. The conical shape is engineered to maximize the efficiency of this separation.
During high-speed spinning, the force pushes the denser components of the sample, like cells, cellular debris, or precipitated proteins, toward the bottom of the tube. The tapered design directs all of this solid matter, often called the pellet, into a very small, concentrated point at the tube’s tip.
The highly concentrated pellet is much easier for a researcher to see and recover without mixing it back into the liquid. The liquid layer remaining above the pellet, known as the supernatant, can then be carefully removed using a pipette. This clean separation and ease of retrieving the concentrated material are why the conical tube is the industry standard for pelleting and purifying biological samples.
Standard Sizes and Common Laboratory Uses
Conical tubes are manufactured in several standard sizes, with the 15-milliliter (mL) and 50-mL volumes being the most common and recognizable in the laboratory. The 15-mL tubes are frequently used for routine work, such as processing smaller blood or urine samples, while the 50-mL tubes accommodate larger volumes, often required in cell culture applications. Smaller versions, such as 1.5-mL and 2-mL tubes, known as microcentrifuge tubes, are also widely used for molecular biology applications requiring minimal sample quantities.
Beyond their primary role in centrifugation, conical tubes serve numerous other functions within the laboratory, including:
- Short-term or long-term storage of reagents, buffers, and biological specimens, especially in freezers.
- Mixing reagents by vortexing or inversion without the risk of spillage, due to their secure screw caps.
- Preparing serial dilutions.
- Safely transporting biological samples between laboratories.
- Temporarily holding waste liquids.