Principles of sterilization and disinfection
Liquids and gases can also be sterilized by filtration. Most of the available filters catch only bacteria and fungi, but with ultrafine filters viruses and even large molecules can be filtered out as well. With membrane filters, retention takes place through small pores. The best-known type is the membrane filter made of organic colloids (e.g., cellulose ester). These materials can be processed to[...]DOWNLOAD REFERAT
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In conventional depth filters, liquids are put through a layer of fibrous material (e.g., asbestos). The effectiveness of this type of filter is due largely to the principle of adsorption. Because of possible toxic side effects, they are now practically obsolete.
Ethylene oxide. This highly reactive gas (C2H4O) is flammable, toxic, and a strong mucosal irritant. Ethylene oxide can be used for sterilization at low temperatures (20-60 ºC). The gas has a high penetration capacity and can even get through some plastic foils.
One drawback is that this gas cannot kill dried microorganisms and requires a relative humidity level of 40-90% in the sterilizing chamber. Ethylene oxide goes into solution in plastics, rubber, and similar materials, therefore sterilized items must be allowed to stand for a longer period to ensure complete desorption.Aldehydes. Formaldehyde (HCHO) is the most important aldehyde. It can be used in a special apparatus for gas sterilization. Its main use, however, is in disinfection. Formaldehyde is a water-soluble gas.
Formalin is a 35% solution of this gas inwater. Formaldehyde irritates mucosa; skin contact may result in inflammations or allergic eczemas. Formaldehyde is a broad-spectrum germicide for bacteria, fungi, and viruses. At higher concentrations, spores are killed as well. This substance is used to disinfect surfaces and objects in 0.5-5% solutions. In the past, it was commonly used in gaseous form to disinfect the air inside rooms (5 g/m3). The mechanism of action of formaldehyde is based on protein denaturation. « mai multe referate din Medicina