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Choosing the right centrifuge

A centrifuge is a device used to separate mixtures made up of parts with different densities. In the medical field, centrifuges are mainly used in laboratories to prepare samples for analysis. For example, a centrifuge is used to separate plasma from blood. They are equipped with a rotor in which the samples to be prepared are placed.

There are different types of centrifuges on the market. Each type is linked to one or more specific applications. It is therefore very important to take this into account when choosing a centrifuge.

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  • What are the different types of centrifuges?

    We can distinguish between:

    • “Standard” centrifuges: most models are versatile and can be used for urinalysis, stool analysis, etc. They have a rotational speed of between 5,000 and 15,000 rpm.
    • Microcentrifuges: these are generally used for small sample volumes, such as capillary tubes for example. They are mainly used for blood work. Their rotational speed is greater than 10,000 rpm. These centrifuges have a compact design.
    • Ultracentrifuges: these are very high-speed centrifuges. They are generally used for advanced analyses in specialized laboratories or in a research context. Their rotational speed is between 50,000 and 100,000 rpm.
    • Manual centrifuges: they  work using a crank operated by a person. Their rotational speed is a maximum of 3,000 rpm.
  • What different functions does a centrifuge have?

    Depending on the type of centrifuge and the intended uses, it can have the following functions:

    • In hemology: there are hematocrit centrifuges and centrifuges for blood banks. These compact centrifuges effectively determine blood’s erythrocyte volume fraction. They can often accommodate 24 capillaries at the same time and their maximum rotational speed is generally 12,000 rpm.
    • In molecular biology: you might want to consider buying centrifuges for DNA extraction for example. In this case, depending on the type of samples you’re working with, you might require a refrigerated centrifuge. Refrigerated centrifuges are used to process samples that need to be kept at a constant temperature. It is therefore essential that they operate at maximum speeds while maintaining the same temperature. In most cases, the temperature range offered by these centrifuges is between -20 and -40 degrees Celsius, which makes them ideal for DNA or RNA analysis, for example.
    • In bacteriology: centrifuges are used for the cytology of liquids from different sources, for example.
    • In parasitology: centrifuges are used to perform parasite concentration tests.
    • In toxicology, pharmacology, etc.
  • How to choose the appropriate rotor?

    There are several types of rotors available. The most common are:

    • Fixed angle: these rotors are made of metal blocks with wells dug inside and inclined at an angle of 15 to 35 degrees to the horizontal, depending on the model. The tubes to be centrifuged are deposited in these wells. In general, these rotors are relatively compact and it is easier to rotate them quickly because of their relatively short radius. Particles tend to sediment mainly along the wall of the tube and towards the bottom of the tube. Most medium and high speed centrifuges use this type of rotor.
    • Swing rotors: they allow the tube to change angles during the stroke. The buckets are vertical when stopped and horizontal when operating. The particles can therefore sediment directly at the bottom of the tube without ever hitting the tube walls. The main disadvantage to this type of rotor is that it cannot reach very high rotation speeds because the buckets in horizontal position extend beyond the radius of the rotor. They are frequently used for low-volume research applications.

    In order to choose the appropriate rotor, it is important to consider the following points:

    • The capacity: how many samples the rotor can hold
    • The speed: varies according to the type of rotor you choose. Much higher speeds can be achieved with fixed angle rotors than with swing out rotors (see previous paragraph).
    • The type of sample to be centrifuged

     

    For diverse applications, it is important to choose a model that will work with different rotors. As such, it is important to ensure that the rotor can be changed easily. Some models are equipped with an automatic rotor identification system.

  • How to choose the best centrifuge configuration?

    The space available in the laboratory in general and on the bench in particular will be the most important element to consider when choosing the centrifuge configuration.

    We can thus distinguish between:

    • Bench-top (compact or not): these centrifuges are small and can be installed on the laboratory bench. Robust, durable and of relatively high capacity, they can run at 5,000/6,000 rpm. Clinical biology laboratories generally have this type of centrifuge. Some models can be refrigerated and thus allow the centrifugation of fragile substances such as certain coagulation factors.
    • Bigger centrifuges are generally floor-standing: if the laboratory wishes to optimize organization and bench space, a floor-standing centrifuge is a wise choice. These centrifuges allow large volumes or a significant number of tubes to be treated. Their rotation speed is high, usually around 30,000 rpm, and they are generally refrigerated. The disadvantage is that they are quite heavy, which must be taken into account during installation.

    It should be noted that refrigerated or ventilated centrifuges require more space than their conventional counterparts.

  • What options are available for centrifuges?

    There are many important features both for ergonomics and for the safety of the user and samples. The following options are available for centrifuges:

    • Refrigerated, non refrigerated, heating
    • Locking centrifuge cover
    • Battery operated
    • Low-noise models or models equipped with a soundproof box
    • Models with or without a timer to set the centrifugation time
    • Tachometer to measure the rotational speed
    • Digital display
    • Possibility of adjusting the rotational speed (acceleration and braking)
    • Self-balancing rotor
    • Autoclavable accessories
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