Tubes and Bottles For Every Application
No single tube design or material will meet all application requirements. A
number of factors should be considered at the time a supply of tubes is
ordered: the particular technique to be used, the nature of the sample
and any solvent or gradient media, the desirability of reusing the tubes,
and certain convenience factors. The properties listed below provide a
guide for anyone involved in the tube selection process.
- Strength and Flexibility, to resist permanent
deformation even when run in fixed angle rotors without tube caps
- Chemical Resistance to a wide range of bases,
acids, and solvents
- Transparency, to permit a clear view of fractions
and bands after centrifugation
- Thin enough to be sliced or punctured after
centrifugation for fraction collection
- Impermeable to Water, to prevent aqueous solutions
from permeating the tube wall and reaching the rotor cavity
- Surface Properties that prevent the adherence
of nucleic acids and proteins
- Temperature Tolerance throughout a wide range
of operating temperatures, without deforming at high temperatures
or cracking when used close to 0°C
- Autoclavable, for convenient sterilization and reuse
- Contaminant-free, to avoid leaching extraneous materials into the sample,
especially materials visible in the sensitive 240-280 nm range
- Odor-free, for pleasant handling
The full line of Beckman Coulter tubes includes a number of tube materials,
each with its own distinct combination of properties, to meet a variety
of application requirements. Available are transparent, translucent, and
opaque tubes, tubes that can be sliced or punctured, tubes that can be
sterilized and reused, and tubes that are resistant to a variety of chemical
compounds.
Tube Selection Considerations
Compatibility of Tube Material with Solvents and Sample
The chemical compatibility of the tube materials with the gradient-forming
medium or other solvent is a prime consideration. Neutral sucrose and
salt solutions cause no problem. But alkaline solutions, such as those
frequently used for the separation of single-stranded forms of DNA, cannot
be used in Ultra-Clear™ tubes or polycarbonate tubes and bottles. Sometimes
DMSO is used in preparation of sucrose gradients for sedimentation of
denatured RNA. Polycarbonate and Ultra-Clear tubes are incompatible with
DMSO, so polyallomer tubes should be used.
The last column of the "Quick
Reference Chart to Tube Materials and Their Properties" shown
below gives some guidelines to the chemical resistances of the various
tube materials. It must be emphasized, however, that other conditions
of centrifugation (g-force, duration of run, etc.) have
considerable effect on how well a tube material will withstand a
particular solvent. Beckman Coulter publication IN-175, "Chemical
Resistances for Beckman Coulter Centrifugation Products", provides
more detailed information about the chemical resistances of the
various tube materials. The wisest course is to test any questionable
combination under operating conditions before making the actual
run.
The type of sample, in some cases, will affect selection of a specific tube
material. DNA, in its denatured or single-stranded form, will adhere to
the surface of some tube materials. Polyallomer would be the best choice.
(Most of this work is done in highly alkaline media which are incompatible
with polycarbonate.)
Lipoprotein separations are most often done in Ultra-Clear tubes because they
are clear and sliceable; these properties simplify fraction location and
recovery by tube slicing. When small lipoprotein samples are to be recovered
by a fractionating device and clear tubes are desirable, there are alternatives:
cellulose propionate, polycarbonate, and Ultra-Clear tubes.
Hazardous materials, either pathogenic or radioactive, should be centrifuged
with extreme care. All possible precautions must be taken to avoid leakage
of the sample into the rotor cavity during centrifugation.
To determine the optimum tube material for your specific sample and gradient
medium, refer to the quick reference chart.
Gradient Formation and Fractionation
When choosing a tube for a density gradient run, some thought should be given
to gradient formation and fractionation. If the bands or zones formed
during centrifugation are indistinct, they may not be visible through
a translucent material such as polyallomer. If optimum band visualization
is important, Ultra-Clear tubes or tubes of polycarbonate or cellulose
propionate should be used. Whenever collection of bands or zones must
be done by puncturing the tube or slicing, a thin, flexible tube wall
is required. Ultra-Clear or Polyallomer tubes should be used, depending
on the need for transparency.
As there are currently no wettable plastic centrifuge tubes available, gradients
should be loaded into plastic tubes from the bottom up to avoid mixing.
High Temperature Centrifugation
Although modern centrifuges and rotors can operate at temperatures as
high as 45°C, one cannot assume that every tube can be safely run over
25°C. Stainless steel and glass are the only materials which will not
experience some deformation when subjected to high temperatures and long
centrifugation times. Plastic tubes undergo some degree of softening at
temperatures higher than 25°C. Whether or not this will cause permanent
deformation is not a question of temperature alone. The centrifugal force
field used, the duration of the centrifugation, the type of rotor, and
even the tube angle all have an effect.
It's obviously impossible to give exact temperature limits for plastic tubes
when so many other variables are involved. The safest policy is to pretest
the tubes under the actual experimental conditions, but with water, rather
than a valuable sample.
Tube Sizes
Tube sizes as indicated in the following charts are nominal sizes, and may
vary somewhat from actual filling capacities. If a thick-walled tube is
run uncapped, the maximum filling volume will depend on the tube angle
of the rotor to be used. See appropriate rotor instruction manuals for
maximum filling levels of tubes.
Tube Cleaning, Sterilization, and Reuse
If tubes are to be reused, special care must be taken during cleaning and sterilization.
All tubes can be washed by hand with a mild detergent such as Solution
555™ diluted 5-to-1 or 10-to-1 with water. This is particularly important
for polycarbonate tubes and bottles which should not be exposed to a detergent
with a pH higher than 8. Tubes and bottles should not be washed in commercial
dishwashers as the detergents and high temperatures are too harsh. Solvents
such as alcohol or acetone react unfavorably with many tube materials.
If an organic solvent must be used in the cleaning procedure, consult
bulletin IN-175, "Chemical
Resistances for Beckman Coulter Centrifugation Products" for a table
of tube material/solvent compatibilities.
The method chosen for sterilization has direct bearing on the number of reuses
one can expect from a tube. Tubes and bottles of polyallomer, polyethylene,
and glass can all be autoclaved, although in general, cold sterilization
methods are not as harsh as autoclaving. Cold sterilization is recommended
for both polycarbonate and Ultra-Clear. Do not dry tubes, bottles, or
accessories in an oven. Labware should be air dried. OptiSeal, Quick-Seal,
Ultra Clear, and thinwall Polyallomer tubes are intended for one-time
use and should be discarded after use.
If maximum reuse is a major consideration, either polyallomer (preferably thick-walled)
or polycarbonate tubes and bottles should be selected, and cold sterilization
methods used. If these tubes are run completely filled in swinging bucket
rotors, most of them can be reused a number of times. Chances of permanent
deformation will be greater whenever the tubes are run in fixed angle
rotors, without caps, and/or partially filled. All of these conditions
tend to stress the centripetal edge of the tube unduly. All tubes that
have been used or autoclaved previously must be individually examined
for signs of deformation or cracking before using them again.
Tube Closures
When other considerations have been resolved, convenience may be a deciding
factor. Without a doubt, the most convenient tube closure is none at all;
none are required for tubes run in swinging bucket rotors and in the Airfuge®
Air-Driven Micro-Ultracentrifuge.
For tubes run in fixed angle rotors, alternatives to the standard tube cap
assemblies are available. Bottles have three-piece cap assemblies which
are easier to use than the more complex tube cap assemblies. Polycarbonate
bottles are available for general-purpose fixed angle rotors, and are
used frequently for differential centrifugation where band recovery is
not a problem. Thickwall tubes can be run in all fixed angle rotors without
caps, provided they are partially filled. (Refer to rotor manuals for
more information on fill volumes.)
When closed tubes are required, Beckman Coulter offers some innovative and
convenient options.
OptiSeal™ Tubes
For virtually effortless sealing, OptiSeal tubes offer the best option.
You simply insert the tube plug and press, and an O-ring seals securely
against the tube's inner surface. During centrifugation, the combination
of g-force and hydrostatic pressure ensures an effective seal.
Engineered for reliability, there are no tools or mechanical parts to
maintain. Finger pressure is all that is needed.
Quick-Seal® Tubes
Quick-Seal Dome-top Tube (top)
Quick-Seal Bell-top Tube (bottom) |
These tubes eliminate most of the steps involved in capping tubes and cut handling
time in half. The top of the Quick-Seal tube is either dome-shaped or
bell-shaped with a 3 mm-long inlet through which the tube is filled. The
filled tube is heat-sealed using the hand-held sealer. The highly reliable
seal achieved makes these tubes ideal for sample storage and for working
with radioactive or pathogenic samples.
There are two Quick-Seal tube designs, dome-top and bell-top. The bell-top
simplifies removal of materials that float upon centrifugation. The dome-top
tubes hold more volume than their bell-top equivalents.
A Quick-Reference Chart to Tube Materials and Their Properties
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