Centrifuges are an integral part of a laboratory and play a key role in the success of an analysis. However, it is a challenging task to select the right centrifuge for a given application.
There are different types of centrifuges available, ranging from mini-centrifuges holding only a few small tubes and spinning several thousand RPM to high-capacity centrifuges capable of handling up to 6 liters of samples and ultracentrifuges with a rotational speed of up to 100,000 RPM.
Additional features such as refrigeration, further complicate the process of selecting the right centrifuge.
This article discusses four questions to help users to successfully identify a general-purpose benchtop laboratory centrifuge.
Do your samples need to be refrigerated?
Ventilated and refrigerated are the two major types of centrifuge. In a ventilated centrifuge, air is drawn into the bowl and then exhausted out of the unit, thereby keeping the bowl contents at a temperature slightly higher than the surrounding temperature in the laboratory.
In this centrifuge, the sample temperature will increase during a typical 10-minute cycle, but the increase is expected to be in the range of several degrees. This type of centrifuge is suitable for applications that do not rely on precise temperature control.
Ventilated centrifuge airflow
A refrigerated centrifuge is a good option for application where precise temperature control is critical, or a lower internal temperature is required during operation. A cooling system is included into a refrigerated centrifuge to lower and keep a preset temperature during operation.
It should be remembered that ventilated centrifuges are not inferior to refrigerated centrifuges, but it is only that they are not the ideal solution in areas where precise temperature control is critical.
A refrigerated centrifuge is sealed and can function at higher RPM owing to the ability to reduce the heat produced by higher rotation speeds. Since a refrigerated centrifuge has a large footprint and high cost, it is not recommended to use it for applications that do not require temperature control.
What are your speed requirements?
A refrigerated centrifuge can operate at higher speeds compared to a ventilated system. However, the optimum speed of a centrifuge might be significantly more than is required for a given laboratory’s needs.
With increasing speed, lighter materials move closer to the rotational axis and denser materials migrate further away. Hence, the speed required for a specific application is more significant than the optimum speed of a centrifuge, especially in cases such as plasma separation from RBCs.
Besides having an optimal speed range, centrifuges should have the ability to utilize rotors suitable for applications within that speed range. Sample tubes are supported by rotors when a centrifuge is operated.
Angular rotors and swinging bucket rotors are the two major types of rotors. Sample tubes are held in buckets in a swinging bucket rotor. The buckets rotate at an angle increasing toward at right angles to the rotational axis under centripetal force with increasing rotor speed. Swinging bucket rotors are ideally suited for low-speed, high capacity applications.
Swinging bucket rotor
A fixed angle rotor holds sample tubes at a constant angle, typically 45 degrees, during operation of a centrifuge. It is capable of rotating at a speed as much as three to four times higher than a swinging bucket rotor spinning the same tubes. What needs to be spun and at what speed are the two important questions based on which the rotor is selected.
Fixed Angle Rotor
What size tubes are you using?
The capacity of a centrifuge is also an important factor as a centrifuge can only hold a fixed number of sample tubes during a run. Therefore, it is important to know how many tubes need to be spun at a time and of what size in order to select the appropriate centrifuge.
However, many different sized tubes can be held by a swinging bucket rotor due to the presence of inserts within the buckets. Increased capacity is another advantage of a swinging bucket rotor. For example, a bucket rotor is capable of holding twenty 50 mL tubes compared to the limit of only 8 tubes of the same size for an angular rotor.
Conical tubes must only be used in an insert designed for conical tubes.
Further, rotors or inserts are intended for use with either round, flat-bottom, or conical tubes only. Therefore, correctly shaped tubes must be used for the rotor or insert selected in order to provide a proper support to the tubes and samples. During operation of a centrifuge, an incorrectly shaped tube can be broken down by centrifugal force.
Do you have size limitations for your centrifuge?
The dimensions of a centrifuge need to be considered due to space constraint. The smallest centrifuges should be used on the bench only. The largest centrifuges are typically too large to be mounted on a bench and therefore, should be floor-mounted only. Mid-sized centrifuges can be mounted either on the bench or on the floor.
Consider available bench or floor space when selecting a centrifuge.
Compared to bench-top centrifuges, floor-mounted centrifuges are often smaller in width and length but taller. Bench-top centrifuges are often shorter than a floor-mounted centrifuge, but larger in width and length. The size of a refrigerated centrifuge is more than that of an equivalent ventilated centrifuge, and therefore extra space is needed for ventilation around the unit.
In summary, several factors need to be considered before selecting the right centrifuge for a given application. In addition to the aforementioned factors, other factors such as warranty, features, and price should also be considered before purchasing an appropriate centrifuge.
User-friendliness is another factor that should be taken into consideration. The centrifuge can be operated by both novice and experienced users without any difficulty, completing tasks without causing any risk to the samples.
Since most of the protocols performed by technicians will be designed by a laboratory manager or researcher, risk can be mitigated when centrifuges with programming ability are used as they allow a sample run with a click of a button.
After selecting a centrifuge provider, users should be able to provide a list of all of their specifications to the supplier and then rely on its expert guidance to identify an appropriate centrifuge.
NuAire laboratory equipment supply
NuAire is involved in the manufacture of ergonomically designed scientific laboratory instruments, offering product, personnel, and/or environmental protection in critical research environments. The laboratory instruments offered by NuAire include:
Biological safety cabinets. Animal research products. Laminar airflow products
CO2 incubators. Centrifuges. Ultra-low temperature freezers
Polypropylene fume hoods and casework
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You can depend on our products to feature brilliant but practical design, and we pay keen attention to every step of the production process, from fabrication to assembly to thorough testing. As a NuAire customer, you can also rely on us for outstanding value and dependable service - the cornerstones of our reputation as the leading provider of laboratory products internationally.
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With over 300,000 square feet of manufacturing space, including a state-of-the-art robotic sheet metal facility, NuAire is able to provide employment to 300 Minnesota families and 60 North American sales representatives, and our manufacturing labor is 100% American.
We also purchase our materials from over 500 American vendors, each operating principally in the United States. More than 60% of the raw materials, parts, and supplies for our products originates in the U.S., and an average of 20-30% of the stainless steel flats we use are made from recycled metal.
While NuAire is an American company, we also have several international business partnerships, which allow us to better serve you, the global laboratory community. NuAire recently started manufacturing a line of Biological Safety Cabinets in China in order to supply products to the Asian markets via Techcomp, Ltd., a publicly traded Chinese company.
In 2014, NuAire founded an international partnership with Hitachi Koki in order to supply high performance centrifuges to the North American market. NuAire can now provide customers with the sales and service of Hitachi High Speed, Ultra, and Micro Ultracentrifuges.
With several other partnerships with a variety of European and Asian companies, we have sold over 100,000 biological safety cabinets to customers in 150 countries and have equipment located on all 7 continents.
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