How to Choose a Desktop Low-Speed Centrifuge

The low-speed benchtop centrifuge is one of the most commonly used basic pieces of equipment, widely employed in hospital laboratories. It is an indispensable tool for tasks such as separating serum from blood, precipitating formed cells, concentrating bacteria, and performing PCR tests, among others.

I. The Working Principle of a Centrifuge

During high-speed rotation, the motion induced by centrifugal force causes solid particles suspended in a liquid to settle out—specifically, particles with greater mass or volume in the suspension move toward the region of the rotor with the greatest radius, while particles with smaller mass or volume tend to deposit closer to the rotor’s inner radius.

Above, we mentioned the concept of centrifugal force. A centrifuge is a machine that generates centrifugal force. The magnitude of centrifugal force depends on the rotor radius, rotational speed, and sample mass—specifically, F = Rmω² (where F is the centrifugal force, R is the radius, m is the sample mass, and ω is the rotational speed). Centrifugal force is one of the most important parameters for evaluating a centrifuge’s performance and also serves as a key criterion for distinguishing between different centrifuge models. When a centrifuge leaves the factory, it will always specify its maximum centrifugal force.

As we all know, the radius of the rotor and the mass of the sample remain constant during operation; only the rotational speed can be varied through control. Therefore, we often tend to use rotational speed as a way to describe a centrifuge—for example, high-speed centrifuge and ultrahigh-speed centrifuge.

II. Classification of Centrifuges

There are many types of centrifuges, and we typically classify them based on the following aspects: By rotational speed, they can be divided into low-speed centrifuges, high-speed centrifuges, and ultrahigh-speed centrifuges. By temperature requirements, they can be categorized as either ordinary centrifuges or refrigerated centrifuges. By rotor type, they are classified into horizontal rotor centrifuges and angle rotor centrifuges. Depending on their size, centrifuges can also be further divided into floor-standing centrifuges, benchtop centrifuges, and pocket-sized centrifuges. Additionally, centrifuges can be categorized by their level of sophistication into ordinary centrifuges and precision centrifuges. Ordinary centrifuges have limited functionality and lack precision in terms of both rotational speed and capacity—for example, the maximum rotational speed of an ordinary centrifuge might be 5,000 rpm, yet its actual operating speed often falls short of this figure. Such centrifuges are suitable only for routine centrifugation tasks, such as separating serum or concentrating urine.
Precision centrifuges offer a wide range of functions and feature precise rotational speeds and capacities, making them ideal for experiments with high demands on centrifuge performance—such as PCR experiments and blood component separation (commonly used in blood banks).

When selecting a standard centrifuge, you should primarily consider two factors—rotational speed and capacity—based on the volume of work involved. Below is a detailed introduction to the key considerations when choosing a precision centrifuge:

(1) Rotational Speed: Centrifuges are classified according to their maximum rotational speed into low-speed centrifuges (<10,000 rpm/min), high-speed centrifuges (10,000 rpm/min to 30,000 rpm/min), and ultrahigh-speed centrifuges (>30,000 rpm/min). Each centrifuge has a rated maximum rotational speed, which refers to the speed under no-load conditions. However, the maximum rotational speed may vary depending on the type of rotor and the mass of the sample being processed. For example, if a centrifuge is rated at 16,000 rpm/min, this means that under no-load conditions, the rotor will spin 16,000 times per minute. Once a sample is added, the actual rotational speed will certainly be lower than 16,000 rpm/min. Different rotors also have different maximum rotational speeds (an imported centrifuge can be equipped with multiple rotors). A horizontal rotor can reach up to 15,000 rpm/min, while an angle rotor typically reaches around 14,000 rpm/min. For specific differences, it’s best to consult the product sales staff and technical personnel from the manufacturer. Therefore, when selecting a centrifuge, you must be careful and ensure that the centrifuge’s maximum rotational speed is higher than your target speed. For instance, if your target speed is 16,000 rpm/min, the centrifuge you choose must have a maximum rotational speed greater than 16,000 rpm/min.

(2) Temperature: Some samples (such as proteins and cells) can be damaged when exposed to high temperatures. In such cases, it’s essential to choose a refrigerated centrifuge, which has a specified temperature range. During high-speed operation, the heat generated by the centrifuge is balanced by its cooling system at a certain temperature—typically, samples subjected to refrigerated centrifugation need to be kept within a temperature range of 3℃ to 8℃. The exact temperature achievable also depends on the rotor used. For example, if a centrifuge has a rated temperature range of -10℃ to 60℃, when equipped with a horizontal rotor, the temperature during rotation can reach around 3℃; however, if an angle rotor is used, the temperature might only drop to about 7℃. It’s important to consult in detail with the product sales representative and the technical staff at the manufacturer regarding this aspect.

(3) Capacity: How many sample tubes need to be centrifuged each time? And how much capacity is required for each sample tube? These factors determine the total capacity of a centrifuge. Simply put, the total capacity of a centrifuge equals the capacity of each centrifuge tube multiplied by the number of tubes. The total capacity should be matched to the volume of work to be performed.

(4) Rotor: Centrifuge rotors are mainly divided into two types. The horizontal rotor keeps the rotor basket in a horizontal position during operation, perpendicular to the rotation axis; samples settle and concentrate at the bottom of the centrifuge tube. The angle rotor, by contrast, maintains a fixed angle between the rotor container and the rotation axis; samples settle and concentrate both at the bottom of the centrifuge tube and along the side walls near the bottom. If you want the separated samples to concentrate exclusively at the bottom of the centrifuge tube, choose a horizontal rotor. If you want the samples to concentrate both at the bottom of the tube and along the side walls near the bottom, choose an angle rotor.

There are also certain special tests or special samples that require specialized rotors, such as large-capacity swinging-bucket rotors (often used in blood banks), enzyme-linked immunosorbent assay (ELISA) plate rotors, slide rotors, PCR rotors, tube rack rotors, and capillary rotors. Each rotor has fixed specifications that are closely linked to the capacity of the centrifuge—for example, a 36×5 ml angle rotor not only determines the type of rotor but also dictates the centrifuge’s capacity. Therefore, selecting the right rotor is extremely important.

(5) Control System: High-end centrifuges are equipped with microcomputer control systems that not only ensure safe operation but also automatically perform various tasks. Nowadays, many centrifuges feature user-friendly control systems, such as rotor identification, safety lock functions, fault-alert indicators, and customizable acceleration and deceleration curves. In addition to these features, it’s important to pay attention to certain details and essential accessories. The main component of a centrifuge is the motor, which comes in two types: brushed motors and brushless motors. Brushed motors have largely been phased out, and today most centrifuges use brushless motors. Some brushless motors even come with built-in braking functions. As for refrigerated centrifuges, there are differences in their cooling technologies; nowadays, environmentally friendly technologies naturally employ fluorine-free refrigeration. Beyond that, noise levels should also be considered—whenever possible, choose a centrifuge with lower noise output to maintain a comfortable experimental environment. When it comes to accessories, caution is key. Certain experiments require specialized centrifuge tubes—for instance, when handling toxic samples or samples needing ultra-high-speed centrifugation—such tubes must be used with appropriate tube sleeves to ensure greater safety. Additionally, some special sample containers (such as irregular-shaped vials or blood bags) demand careful consideration during the selection process. If these details and accessories aren’t properly taken into account, the centrifuge may fail to operate effectively.

The price of the three centrifuges

There’s a significant difference between domestically produced and imported centrifuges. For centrifuges with the same functionality, imported models typically cost about 6 to 10 times more than their domestic counterparts. The main reason is that imported centrifuges are more durable and offer more precise control over temperature and rotational speed. Within the same product category, price differences among centrifuges aren’t substantial; the primary distinctions lie in performance and configuration.

The main difference between centrifuges lies in their performance: refrigerated centrifuges are significantly more expensive than standard ones. Some centrifuges also come with heating functions, and the more sophisticated the control software, the higher the price. A significant difference also lies in the configuration—sometimes the cost of accessories can even exceed the price of the main unit itself. When making a purchase, it’s important to note that, in addition to the main unit, you’ll need to consider the rotor(s)—both in terms of quantity and type—as well as essential items such as centrifuge tubes, tube holders, specialized centrifuge bottles, or blood bags. Only when you add up all these components can you determine the total cost of a complete centrifuge system.