Preparative ultracentrifuges are designed to operate at exceptionally high speeds of up to 150,000 rpm with g-forces as high as 1,050,000 x g. This makes it possible to perform advanced separation techniques, such as the isolation of macromolecules or nanoparticles, fractionation of subcellular components, or purification of vesicles or viral particles. When working with such high speeds, safety is paramount. Thankfully, today’s ultracentrifuges include advanced safety features to protect the user as well as simplify operation. To keep ultracentrifuges functioning at peak performance and to maximize safety and efficiency, researchers should follow recommended best practices for their use and maintenance.
Ultracentrifuges can be fitted with several different types of rotors. These include fixed-angle rotors (which hold tubes at an angle of 22–50o) and neo-angle rotors (with a tube angle of less than 10o), which are most commonly used for pelleting, and vertical and swing-bucket rotors, which are best suited to performing density gradient separations. Multiple tube types are also available, constructed of materials spanning polypropylene and polycarbonate through stainless steel and titanium. Factors to consider for tube selection include the volume, centrifugal force resistance, and chemical compatibility with the sample, as well as whether the tube needs to be sterile, autoclavable, or transparent. It is also important to think about how the tube will be sealed—with a screw cap, inner lid, or via the use of O-rings. Ultracentrifuge manufacturers will be able to offer guidance when it comes to choosing the best option for a specific purpose.
Select the appropriate vessel and rotor for your sample type, volume, speed, and application. Shown: Eppendorf Centrifuge CS150NX with Swing-Bucket Rotor S50ST for 4 x 7 mL PA tubes (nominal volume) has a maximum speed of 253,000 x g (50,000 rpm).
Before running an ultracentrifuge, a visual check is essential to avoid compromising precious sample material, damaging the instrument, or causing unintentional harm. Rotors and rotor covers should be inspected for scratches, corrosion, or dirt, and any threads and rotor packing must be confirmed to be sufficiently greased. In the case of swing bucket rotors, buckets and hooks should be examined for signs of deformation, while the integrity of tubes or other vessels also requires close scrutiny. If a potential cause for concern is observed, it is critical that it be addressed prior to use—either by a trained operative or a qualified service engineer, depending on the nature of the issue.
Visually examine all parts of the rotor prior to use.
Balancing samples properly is one of the golden rules of ultracentrifugation. This means placing identical tubes (with matching lids), volumes, and sample types opposite one another. Ultracentrifuges with a non-contact imbalance sensor ensure safe operation by preventing centrifugation of unbalanced loads.
It is also vital to select a rotor that is compatible with the ultracentrifuge in question and to load it correctly into the instrument chamber. Following placement on the drive shaft, the rotor should be lifted up and down several times to confirm it has been positioned safely and then gently spun by hand to ensure it moves smoothly. Advanced features in some ultracentrifuges such as automatic rotor detection and self-locking rotor systems make changing rotors easy and foolproof.
Where prechilled rotors will be used, the ultracentrifuge should be precooled before the rotor is placed on to the drive shaft and any condensation wiped away with a soft cloth. For swing-bucket rotors, each bucket should be placed in its correct (numbered) rotor position and the bucket number matched to the number on the cap. Importantly, all of the available buckets must be set, even if not all of them will contain samples, and empty tubes should never be used.
Good lab practices, including regular maintenance, safeguard ultracentrifuge performance and will also help extend the instrument’s useful life. Rotors and accessories should be handled carefully, and any accidental spills cleaned up straight away. After centrifugation, the rotor should be removed from the ultracentrifuge and the instrument chamber wiped with a soft cloth to remove any condensation, and the door to the ultracentrifuge should be left open to allow the chamber to dry. Once a month, the ultracentrifuge drive shaft and the corresponding mount within the rotor should similarly be wiped down, and the rotor itself given a more thorough clean. For assured reliability and uptime, an annual preventive maintenance service program by a manufacturer-certified technician verifies the ultracentrifuge is operating to manufacturer’s specifications.
Proper cleaning and maintenance will extend the life of your centrifuge and rotors. Shown: Eppendorf Centrifuge CP100NX
Eppendorf offers a comprehensive selection of ultracentrifuges, including both floor-standing and benchtop options, for high quality sample preparation. To learn more, visit eppendorf.com