Sterilization Processes

Chemical Processes (Gas/Liquid)

Whereas the most widely used traditional chemical processes were based on alkylating agents such as EtO and the various aldehydes, most of the new methods are oxidative processes based on "peroxy" compounds. These include sterilants based on compounds such as hydrogen peroxide, peracetic acid, peroxysulphates, chlorine dioxide, and ozone. For the most part, the microbicidal action of these chemicals has been recognized for many years.

Peracetic Acid. Peracetic acid is currently used in a number of sterilization processes for endoscopes, or use as a liquid sterilant in suitable disinfectors for sterilization of thermolabile endoscopes. Vapor-phase generators employing peracetic acid are being sold for the decontamination, disinfection, or sterilization of products such as isolators.

Peracetic acid is a colorless liquid with a pungent odor, miscible with water. Commercially available as a 35% or 40% solution, it is generally unstable, decomposing to give oxygen, acetic acid, and other degradation products, which include hydrogen peroxide and water.

Acetic acid and hydrogen peroxide are invariably present in low concentration. Peracetic acid is corrosive to certain materials and it is lachrymatory, an irritant, and a vesicant (causing blistering) on prolonged contact. Its use as a sterilant therefore relies on obtaining formulations that inhibit corrosion of sensitive materials and stabilize the solution to give it a usable shelf life.

Hydrogen Peroxide. Hydrogen peroxide as a 3% aqueous solution has long been used as an antiseptic. For example, hydrogen peroxide potentiated by ultraviolet light has been used in the production-line sterilization of commodity items such as cartons for food products.

The deep-vacuum hydrogen peroxide process operates in a manner analogous to gas sterilization processes. Initial air removal allows for rapid diffusion, and humidity is controlled to optimize the microbicidal effect. The process is compatible with a wide range of materials, but traditional packaging is likely to interfere with the process because of its reaction with, or high absorption of, the hydrogen peroxide. Although the process is finding extensive use in the sterilization of lyophilizers, a general-purpose unit is not yet available.

Ozone. The bactericidal and sporicidal effect of ozone has long been recognized. Its use as a sterilant, however, has been limited because of its instability, which precludes storing it ready for use, and because of the difficulty of generating pure ozone. Ozone is produced naturally by the effect of sunlight or ultraviolet light on oxygen, and also by electrical discharge. Recent technological advances have made the generation of ozone a more practicable proposition, and commercially available sterilizers have been developed. The Cyclops Co. has introduced a machine for sterilizing endoscopes that pumps humidified ozone through the unit. Advantages of the system are said to include freedom from long-term toxic residuals and ease of use, with only medical-grade oxygen and electrical connections required. Potential disadvantages include the reactivity of ozone with certain materials.

Chlorine Dioxide. Chlorine dioxide (ClO₂), which is a gas at temperatures above 11°C, is another chemical that has long been known to have microbicidal properties and that has, like ozone, been used in water purification systems. The germicidal and sporicidal properties of chlorine dioxide have been recognized since long.

Many disinfection technologies employ chlorine dioxide in aqueous solution and, when necessary, use nitrogen or air purging to remove the traces of residual gas. The major problems with this technology have always been that chlorine dioxide gas cannot be safely liquefied or stored under pressure for transport and subsequent use (since under these conditions it is explosive), and that as an aqueous solution it is unstable and corrosive.  

Disclaimer

The content of this issue is presented for general information only as perceived by the writer of the article. Reader should independently verify the correctness and accuracy of the material before using the same for any purpose whatsoever. The Company or Management or Staff of Puneet Industries or the Writer shall not be responsible for any inaccuracy or error in the article.

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