INTRODUCTION AND BRIEF HISTORY
One of the most important pieces of equipment in the laboratory is the centrifuge, which facilitates the separation of samples of different densities. Centrifuge exists in different forms for different utility: gas centrifuge for isotope separation, human and non-human centrifuges for aeronautics and astronautics, industrial centrifuge separator as a coolant filtration system, geotechnical centrifuge for testing Geotechnical Engineering systems, and various centrifuges for commercial applications such as washing machines and sugar centrifugal machines.
The use of centrifuge systems started as early as mid-15th century when hand-driven centrifuge was used as a milk separator, and in 1864, Antonin Prandtl developed the first dairy centrifuge which separates the cream from milk. The potential of using the centrifuge system in the laboratory was exploited in 1869 by Friedrich Miescher. He was the first researcher to isolate nucleic acid from a cell with the use of a crude centrifuge system. The use of the centrifuge in the laboratory was then recognized and further developed which led to the development of a continuous centrifugal separator by Gustaf de Laval. The commercialization of centrifuge then surfaced as further improvements on the centrifuge system were made, such as Theodor Svedberg’s ultracentrifuge which enabled him to record sedimentation boundaries, Emile Henriot’s centrifuge which had very high rotational speeds, and many more.
CHOOSING THE BEST CENTRIFUGE
With the vast choices in the market, you should be able to know how to choose the right and best kind of centrifuge. Keep three parameters in mind while selecting a centrifuge.
- Your needs
- Total cost
It is important to know your needs before buying a centrifuge because, for every application, there is a right and best kind of centrifuge available. The most common applications that utilize centrifuge systems are medical and laboratory works. Most commonly microcentrifuge, benchtop centrifuge, high-speed centrifuge, ultracentrifuge, and hematocrit centrifuge are used in these fields. For example, ultracentrifuge is commonly used in extracting cellular components, such as DNA, in molecular biology, microbiology, and biochemistry. Hematocrit units, on the other hand, are mostly used to separate blood components into the plasma and RBC layer.
Some of the specifications that you should be taking into account are:
- Speed and performance (revolutions per minute and relative centrifugal force)
- Instrument capacity
- Ease of operation
The rate of centrifugation, usually expressed as revolutions per minute (RPM), is used by the manufacturers to describe how fast the centrifuge is rotating, regardless of the size of the rotor. On the other hand, the relative centrifugal force (RCF) is the force from the revolutions of the rotor that is exerted on the contents of the rotor which causes the separation of aqueous solutions in the centrifuge. These two are one of the most significant features to consider in choosing centrifuges because the need for the centrifugal force varies for the sedimentation of various samples. For example, to properly separate certain bacterial cells from a sample, high speed or ultracentrifugation is needed.
Some centrifuges have fixed speed, while others offer variability due to control panels or rotary systems that enables the user to designate a specific speed or power. This variable-speed feature and rotary selection allow users to utilize their centrifuge for various applications (multipurpose centrifuge).
Instrument capacity refers to the maximum amount or volume of samples that you can fit inside the rotor. Generally, for microcentrifuges, the volume of the sample that it can take is only up to 5.0 mL per tube or vial. However, some models of Eppendorf can accommodate tubes with volumes of up to 50 mL. The number of tubes or vials per rotor varies among models of microcentrifuges. The number and type of samples each centrifuge can accommodate depends on the type of rotor of the centrifuge, and in some models, these rotors can be replaced with some models having up to 18 rotor options. Some centrifuges are also equipped with systems for refrigeration, which are useful for temperature labile samples.
On the ease of operation, there are different types of control panels and programs that a centrifuge can have. You should opt for buying models with controls that are user-friendly if you are not used to handling centrifuges so that you would be able to use the centrifuge properly and to avoid errors that could lead to disasters in the working place. Some centrifuges have alarms, safety locked lids, and automatic rotor identification that could help in the ease and safety of performing centrifugation while multitasking with other laboratory works.
It is important to take note that the higher the power of the centrifuge, the higher the energy it needs, hence it is less energy-efficient than the low-speed ones. However, some models are more budget-friendly that could still produce satisfactory results, albeit not as accurate as expensive high-speed centrifuges. Another important thing is that some models can be bought with or without rotors; you have to buy the rotors separately if the rotors are not included in the model. Also, the warranty of the product should be taken into consideration in case things proceed the way you didn’t anticipate.
List of Best Microcentrifuges
The main advantage of microcentrifuges, as the name suggests, is the compact footprint it provides. Based on the parameters mentioned above, reviews of users, and nominations or awards won by the apparatus, here is our list that you can choose from:
Eppendorf® Research Plus Multichannel Pipette
Speed and performance – Variable speed/adjustable speed: 800-13,200 rpm; max RCF of 16,100 x g
Instrument capacity – 24 1.5 ml and 2 ml tubes or 36 0.5 ml tubes
Rotor options – 3 options (Rotor not provided)
Ease of operation – keypad control type; user-friendly control knobs; digital display of time and speed with setting in RPM and RCF
Extra feature/s – Refrigeration: compact cooling system and Fast Temp function
Power – 120V/60Hz
This model offers refrigeration, for applications that require certain temperature levels. It can cool the chamber up to 4ºC in 16 minutes with its Fast Temp function. Also, it is important to mention that this is also a multipurpose centrifuge with variable settings at your disposal which can be adjusted with the use of keypad and control knobs. It can also maintain perfect temperatures even if operating under maximum RCF.
Eppendorf Model 5424
Speed and performance – Variable speed; Maximum molecular grade speed of 21,130 x g
Instrument capacity – 24 x 1.5/2.0 mL; 4 x PCR 8-tube strip
Rotor options – 4 options
Ease of operation – Rotary knobs for quick and easy input of settings; five-digit speed display
Extra feature/s – Short spin speed setting; soft braking; adjustable volume alarm
Power – 120V/60Hz
This model offers no cooling system (but the model 5424 R does) but serves its purpose well in centrifugation with high maximum RCF and adjustable speed. This centrifuge also has a specific contoured rotor bowl design to reduce noise, called OptiBowl. It is easy to use with its five-digit speed display, keypad system, and rotary knobs and includes a certified aerosol-tight rotor. Also, this model has an adjustable volume alarm and soft brakes.
Labnet C0160 Spectrafuge
Speed and performance – Variable speed; minimum speed of 1,000 RPM; maximum speed of 14,000 RPM
Instrument capacity – 18 place rotor for 1.5 ml and 2.0 ml tubes or smaller tubes with adapter
Rotor options – 1 option
Ease of operation – Control knobs for easy setting of speed and time
Extra feature/s – Timer range of 1-30 minutes; quick button allows momentary runs
Power – 120V/60Hz
This model also offers no cooling system, but for applications that require sub-ambient temperatures, this model can be operated in rooms with relatively low temperature. This high-speed microcentrifuge’s rotor can accommodate a minimum of 1.5 ml volume of samples per tube. However, with the use of adapters, like the StripSpin rotor adapter, it can hold two 8 x 0.2 ml strips.
HWLAB Multi-Speed Desktop Mini Centrifuge
Speed and performance – Speed range: 4,000 RPM, 6,000 RPM and 10,000 RPM; Maximum RCF are 770 x g, 1,700 x g and 4,800 x g
Instrument capacity – circular rotor: six 0.2 ml, 0.5 ml, and 2.0 ml tubes; strip rotor: sixteen 0.2 ml tubes
Rotor options – 2 options
Ease of operation – Buttons at the front panel for easy setting of speed.
Extra feature/s – Offers three-speed options
Power – 100V-240V/50Hz-60Hz
This centrifuge offers three different speed settings. It also has two rotor options, and both are fixed-angle rotors. The circular rotor offers more volume capacity but less number of tubes: six 0.2ml, 0.5ml, and 2.0 ml tubes. On the other hand, the strip rotor can accommodate sixteen tubes but with only 0.2 ml volume capacity.
Scilogex D2012 Personal Micro-Centrifuge
Speed and performance – Variable speed; 200-15000 RPM; 15200 x g RCF
Instrument capacity – 12 place rotor; 2mL x 12; 0.2mL and 0.5mL adapters available
Rotor options – 3
Ease of operation – Large LCD; coarse speed setting; fine speed controlled by triggers
Extra feature/s – Brushless motor drive; Over-speed detection; Automatic door lock
Power – 110V/60Hz
This model will produce significant results, given that its maximum RCF is 15,200 x g and it has over-speed detection to protect your samples. This model also provides variety in volumes of samples, with a maximum volume of 2mL. It has a brushless motor drive that requires little to no maintenance and has over-speed detection and automatic door lock for the safety of the user and the samples. With a 2-year warranty, this product will be worth the price and would not disappoint.
Bio Lion XC-10K Mini Desktop Centrifuge
Speed and performance – Fixed/single speed; 10,000 RPM; 5,000 x g RCF
Instrument capacity – circular rotor: 6-place with 0.5ml, 1.2ml, or 1.5 ml tubes; strip tube rotor: 16-place with 0.2ml tubes
Rotor options – 2 options
Ease of operation – Buttons on the front panel for easy setting of controls
Extra feature/s – Palm-shaped lid; automatic stop for safety
Power – 100-240V/50-60Hz
TAKING CARE OF CENTRIFUGES
Every centrifuge comes with a manual, and it includes information on cleaning, maintenance, and possibly lists of disinfectants which are safe to use. Manuals should be read beforehand and should be kept for future reference.
The materials used in the manufacturing of centrifuges vary; plastic, ceramic, aluminum, and stainless steel are most commonly employed. Refer to the manual for recommendations from the manufacturers on chemicals and equipment to use. Make sure to clean the centrifuge daily, or at least weekly, to ensure the longevity and durability of the item. Remove the rotor, container holders, and samples, before cleaning the interior of the centrifuge. Clean the interior bucket, specimen holder, rotary motors, and other parts of the centrifuge. Do not use caustic detergents or anything with chlorine as disinfectant or sterilizer, nor should you use steel wool, wire brushes, and other abrasives, when cleaning the centrifuge. Use a sponge and water with mild detergent instead.
Remember to clean the exterior too. Never pour water directly, or flood the interior of the centrifuge with water. This will damage the sensors, wirings, and other parts of the centrifuge that are sensitive. After cleaning, make sure to dry each part and cavity of the centrifuge properly.
Samples and Spills
Do not centrifuge uncommon solvents or solutions without referring to the manual first. Handle the human blood samples with utmost care and precaution to avoid contamination.
The spilled sample on the rotor will be dispersed as a mist if the centrifuge is running. However, many rotors have sealed compartments that provide aerosol containment to detain the mist. Decontamination of the containers must be done immediately. If the model does not offer the sealed compartment, then the whole chamber must be disinfected.
The forces exerted by the centrifugal field take a toll on the rotor. Do not attempt to run the rotor at speeds higher than its maximum. Refer to the manual for specific instructions for handling rotors and make sure to replace damaged rotors (if applicable) before using a centrifuge.
During centrifugation, containers of the samples like glass tubes can break due to the force exerted by the system. Any fragments of the glass or spillage from the sample should be removed from the buckets, adapters, rubber liners, and rotor chamber before using the centrifuge again. Remember to do several dry runs without samples to ensure that there is no further damage, and clean the dust that might have come from sandblasting of the rotor chamber due to glass fragments between each run.