Chemical compatibility of tube materials with gradient-forming media or other solvents is a prime consideration.
- Neutral sucrose and salt solutions typically present no issues
- Alkaline solutions such as those used for separating single-stranded forms of DNA should not be used in Ultra-Clear™ or polycarbonate tubes and bottles
- If DMSO is used to prepare sucrose gradients for sedimentation of denatured RNA, operators should use polyallomer tubes.
It is advisable to always test any questionable material/media combination under operating conditions prior to the actual run. Conditions such as g-force, duration of run, etc. can have considerable effect on how tube material will perform/withstand a particular solvent.
Sample types may affect tube material differently
- Single-stranded or denatured DNA will adhere to the surface of some tube materials requiring the use of a polyallomer tube as much of this work is done in highly alkaline media incompatible with polycarbonate
- Lipoprotein separations are typically done in super-clear and sliceable Ultra-Clear tubes to simplify fraction location and recovery
- Cellulose propionate, polycarbonate and Ultra-Clear tubes may also be used when recovering small lipoprotein samples with a fractionating device
Use extreme care when spinning hazardous materials, either pathogenic or radioactive. All possible precautions should be taken to prevent any leakage into the rotor cavity during centrifugation.
Gradient formation and fractionation
When choosing a tube for a density gradient run, some thought should be given to gradient formation and fractionation.
- If optimum band visualization is important, Ultra-Clear tubes or tubes of polycarbonate or cellulose propionate should be used
- Whenever band or zone collection is performed by puncturing or slicing, a thin flexible tube wall is required
- Gradients must be loaded into plastic tubes from bottom up to avoid mixing
Although modern centrifuges and rotors can operate at temperatures as high as 45°C, it is not advisable to assume that every tube can safely run over 25°C.
- Stainless steel and glass are the only materials which will not deform/degrade when subjected to high temperatures and long centrifugation times
- Plastic tubes undergo some degree of softening at temperatures higher than 25°C. Factor in centrifugal force, duration, rotor type and even tube angle, and deformation may occur
- It’s advisable to pretest under actual experimental conditions with tubes of water to determine any potential negative outcome
Tube sizes noted in the following charts are nominal sizes and may vary somewhat from actual filling capacities. When running a thick-walled tube uncapped, the maximum filling volume will depend on tube angle. Refer to your Rotor Instruction Manual for specific detail regarding maximum filling levels of tubes.
Special care must be taken during cleaning and sterilization of reusable tubes.
- All tubes should be hand-washed with a mild detergent such as Solution 555™ diluted 5-to-1 or 10-to-1 with water. Do not wash tubes or bottles in commercial dishwashers.
- Polycarbonate tubes and bottles should not be exposed to detergents with a pH higher than 8.
- If an organic solvent such as alcohol or acetone must be used in the cleaning procedure, consult the Chemical Resistance Guid for Beckman Coulter Tubes and Bottles for detail on tube material and solvent compatibilities.
- The sterilization method has a direct effect on the number of reuses one can expect from a tube
- Polyallomer, polyethylene and glass tubes and bottles may be autoclaved. NOTE: cold sterilization is less harsh and is recommended for polycarbonate and Ultra-Clear tubes and bottles
- Always air dry tubes, bottles and accessories. Never use an oven to dry labware or other containment accessories.
- OptiSeal, Quick-Seal, Ultra Clear and thin-wall Polyallomer are disposable-format tubes and should be discarded after use
- If re-use is a consideration, polyallomer (preferably thick-walled) or polycarbonate tubes and bottles should be selected and cold sterilization methods used
- Running such tubes completely filled in swinging bucket rotors will accommodate multiple uses
- Potential for permanent deformation will increase whenever tubes are run partially filled, without caps, or in fixed angle rotors
- Tubes that have been used or previously autoclaved should always be inspected for signs of deformation or cracking
Tube closures and convenience
When other considerations have been addressed, convenience may be a deciding factor. Without a doubt, the most convenient tube closure is none at all. No closures are required for tubes run in swinging bucket rotors and in the Airfuge® Air-Driven Micro-Ultracentrifuge.
Alternatives to standard tube cap assemblies are available for tubes run in fixed angle rotors.
- Bottles have three-piece cap assemblies and are easier to use than
- Polycarbonate bottles are available for general-purpose fixed angle rotors and are frequently used for differential centrifugation where band recovery is not a problem
- Partially-filled thick-wall tubes can be run in all fixed angle rotors without caps (Refer to your rotor manual for full detail on fill volumes)
Closed Tube Options
OptiSeal Tubes for virtually effortless sealing
- Insert the tube plug and press
- O-ring seals securely against inner surface of tube
- Combination of g-force and hydrostatic pressure ensures an effective seal during centrifugation
- No tools or mechanical parts
- Highly reliable
Quick-Seal tubes cut handling time in half
Dome-top or tube-top design for maximum flexibility
- Tubes filled through dome-shaped opening with a 3mm inlet
- Tubes are heat-sealed using a hand-held sealer
- Highly reliable seal makes these tubes ideal for sample storage and working with radioactive or pathogenic samples
Note: This information has been consolidated from a number of sources and is provided only as a guide to the selection of tube materials. Soak tests at 1 g (at 20°C) established the data for most of the materials; reactions may vary under the stress of centrifugation, or with extended contact or temperature variations. To prevent failure and loss of valuable sample, ALWAYS TEST SOLUTIONS UNDER OPERATING CONDITIONS BEFORE USE.
Warning: Do not use flammable substances in or near an operating centrifuge.