28 KNOWLEDGE Sterilisation of laboratory equipment made of plastics Autoclaving Autoclaving (steam sterilisation) is defined as the destruction or irreversible inactivation of all reproducible microorganisms under exposure to “saturated steam at a minimum of 120 °C.” (DIN 58946-1, 1987). DIN EN 285 specifies a minimum exposure time (te) of 20 minutes (killing time and safety margin) at a sterilisation temperature of 121 °C. For the correct sterilisation procedure, including biological safety (DIN EN 285), please contact your hygiene specialist. Prior to autoclaving plastic labware, ensure that no soiling or residual contamination remains on the equipment. Otherwise, the residual contamination will bake on solidly during the autoclaving process. Even substances that have no effect on the plastic at room temperature can still lead to destruction of the plastic during the autoclaving process. Additionally, microorganisms might not be killed effectively if they are protected by the residual contamination. Notes on autoclaving • Containers with screw tops or stoppers must be open during autoclaving to allow for pressure equalisation ➡ Autoclaving of a closed container will lead to the deformation or destruction of the container • Plastic labware should be stood upright on a level surface during autoclaving to avoid shape deformation. ➡ Plastic labware should not be laid on its side during autoclaving • No mechanical stresses should be present during autoclaving ➡ For example, do not stack items • Do not autoclave any container that contains residual contamination or even rinsing agent • Not all plastics are resistant to steam sterilisation! For example, polycarbonate loses its tensile strength ➡ Mind the temperature limits for the plastics ➡ Autoclavable products are identified with a “121 °C” symbol in this catalogue The surfaces of some plastics can be attacked by chemicals present during autoclaving, which can cause persistent clouding. Some transparent plastics can absorb minute quantities of steam, which can lead to reversible clouding. This clouding disappears upon drying, which can be accelerated through the use of a drying oven. Note! For gas sterilisation, dry heat, and prior to heating in a microwave oven, all closures and stoppers must be removed as well. Heating plastics in microwave ovens Many plastics are suitable for use in microwave ovens. More accurate information can be obtained from the Table “Physical Properties of Plastics” on page 26. In this connection, it is important to be mindful of the chemical and temperature stability of the various plastics, and to ascertain whether the particular article and its contents are compatible with the given temperature. When aggressive acids, alkalis, or solvents are to be heated, the use of fluoroplastics is recommended. It is very important to provide for adequate ventilation (e.g., fume hoods). Prior to the use of plastic labware in a microwave oven, the closures and stoppers must be removed from the apparatus. Recommended autoclaving protocol 20 minutes at 121 °C (2 bar), according to DIN EN 285
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