Precautions--Use of laboratory centrifuges

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Even with machines of reliable quality, it is necessary to strictly follow the required precautions in order to maximize their performance. As the saying goes, the camp remains steady while the soldiers come and go; in the laboratory, batches of students arrive and then graduate, and strict training is essential to reduce accidents. I still remember that many years ago, in the school, one of the large centrifuges used for experiments broke down, so a foreign expert was called in to fix it. Seeing the stains on the walls of the centrifuge chamber, as well as the pieces of paper or rubber pads left in some of the rotor holes for temporary balancing purposes, and given the careless attitude of the students, the foreign expert muttered that it was hard to believe that graduate students from such a renowned Chinese institution conducted experiments in such a sloppy manner. Similar statements were heard many times over the years; for example, an automatic sequencing needle-based sample loader sent from Shanghai for repair – the fine metal needles used for sampling were supposed to be soaked and cleaned, but instead they were disinfected by heating – the needles became clogged, or were deliberately twisted or broken. At that time, people asked, \"Is this really something used by the best institutions, the best laboratories, and the best students in China?\" I feel utterly ashamed every time I hear it. In fact, the damage to many instruments is simply due to our fear of trouble, carelessness, or a desire to save effort – perhaps no problems arise immediately, but the damage accumulates over time. Being stricter with each student can not only reduce unnecessary damage but also make the experiments proceed much more smoothly. 1. Loading and equilibration of the sample, due to the high centrifugal forces generated during centrifugation. When the sample attached to the rotor is unbalanced, a large torque is generated; in mild cases this causes the machine to shake and vibrate, while in severe cases it can twist the shaft and lead to accidents. Therefore, the balanced loading of centrifuged samples is a matter that requires special attention. The higher the centrifugation speed, the greater the requirement for balance. With the exception of small centrifuges whose rotors are softer and thus have a certain degree of adjustability that allows visual balance checking, all centrifuges require the use of a balance to achieve sample balance. Centrifuge tubes should be symmetrically balanced in pairs, or in groups of three, and it is ideal if they all have the same weight. The horizontal rotor should not run idle. At equilibrium, it is necessary not only to ensure that the two symmetric tube samples have equal weight, but also that their densities and volumes are comparable. This is because the torque generated during centrifugation depends not only on the weight of the sample but also on its rotational radius. For example, although a tube of water and a half-tube of sand have the same weight, the sand has a larger radius of rotation; as a result, the torque differs significantly, and the rotation is not balanced. Therefore, the two centrifuge tubes in symmetric positions must be loaded with samples of similar density. For example, if two samples are to be centrifuged simultaneously, one tube is diluted with distilled water, while the other is prepared using 60% sucrose. Although the two tubes have equal weight, they cannot be used as a pair in a centrifuge; instead, an additional tube of water and another tube containing 60% sucrose must be used as counterweights to ensure proper operation. 2. The storage and use of the rotor must be carried out strictly in accordance with the instructions. 3. The selection of centrifuge tubes should be based on their specifications and materials, to prevent breakage due to improper use; this avoids not only the loss of samples but also contamination of the rotor and the centrifuge. During ultracentrifugation, operations are carried out under vacuum in order to reduce resistance. Therefore, apart from stainless steel and thick-walled polycarbonate (PC) centrifuge tubes, the samples must be filled to capacity; otherwise, the centrifuge tubes may deform or break due to the vacuum. For conventional high-speed or low-speed centrifugation, it is not necessary to fill the container to capacity; all rotors with lids, horizontal baskets, and test tube caps must be tightly sealed to prevent sample leakage and loss of balance. When using an angular rotor, it is necessary to cover the rotor lid; otherwise, significant vortex resistance and frictional heating will occur within the centrifugation chamber, which places additional strain on the centrifuge’s motor and refrigeration system and affects its service life.