What are the Chemical methods of sterilization & Disinfection #sterilization #disinfection
Channel: Harshit meena vlogs
Date: 2022-03-10

https://youtu.be/HQtnu1UnbIo

Chemical methods of #sterilization  - Gaseous and Liquid
1. Gaseous Sterilization
i. Ethylene oxide
ii. Formaldehyde
iii. Nitrogen dioxide (NO2)
iv. Ozone
2. Liquid Sterilization
i. Hydrogen peroxide
ii. Glutaraldehyde
iii. Hypochlorite
What is Chemical Sterilization?
Chemical Sterilization is the process of removal of microorganisms by the use of chemical bactericidal agents.
Even if physical methods of sterilization are more appropriate for effective sterilization, it is not always appropriate to use for heat-sensitive materials like plastics, fiber optics, and biological specimens.
Under such conditions, chemical either in liquid or gaseous state can be used for sterilization. 
1. Gaseous Sterilization
i. Ethylene oxide
Ethylene oxide (EO) gas is a common gas used for chemical treatment applied to sterilize, pasteurize, or disinfect different types of equipment and surfaces because of its wide range of compatibility with different materials.
EO treatment often replaces other sterilization techniques like heat, radiation, and even chemicals in cases where the objects are sensitive to these techniques.
This method is a widespread method used for almost 70% of all sterilizations and around 50% for disposable medical devices.
ii. Formaldehyde
Formaldehyde is another important highly reactive gas which is used for sterilization.
This gas is obtained by heating formalin (37%w/v) to a temperature of 70-80°C.
It possesses broad-spectrum biocidal activity and has found application in the sterilization of reusable surgical instruments, specific medical, diagnostic and electrical equipment, and the surface sterilization of powders.
Formaldehyde doesn’t have the same penetrating power of ethylene oxide but works on the same principle of modification of protein and nucleic acid.
As a result of the low penetrating power, its use is often limited to paper and cotton fabrics.
Formaldehyde can generally be detected by smell at concentrations lower than those permitted in the atmosphere and thus can be detected during leakage or other such accidents.
iii. Nitrogen dioxide (NO2)
Nitrogen dioxide is a rapid and effective sterilant that can be used for the removal of common bacteria, fungi, and even spores.
NO2 has a low boiling point (20°C) which allows a high vapor pressure at standard temperature.
This property of NO2 enables the use of the gas at standard temperature and pressure.
The biocidal action of this gas involves the degradation of DNA by the nitration of phosphate backbone, which results in lethal effects on the exposed organism as it absorbs NO2.
An advantage of this gas is that no condensation of the gas occurs on the surface of the devices because of the low level of gas used and the high vapor pressure.
iv. Ozone
Ozone is a highly reactive industrial gas that is commonly used to sterilize air and water and as a disinfectant for surfaces.
Ozone is a potent oxidizing property that is capable of destroying a wide range of organisms including prions, without the use of hazardous chemicals as ozone is usually generated from medical-grade oxygen.
Similarly, the high reactivity of ozone allows the removal of waste ozone by converting the ozone into oxygen by passing it through a simple catalyst.
However, because ozone is an unstable and reactive gas, it has to be produced on-site, which limits the use of ozone in different settings.
It is also very hazardous and thus only be used at a concentration of 5ppm, which is 160 times less than that of ethylene oxide.
Read also: Physical methods of sterilization
2. Liquid Sterilization
Liquid sterilization is the process of sterilization which involves the submerging of equipment in the liquid sterilant to kill all viable microorganisms and their spores.
Although liquid sterilization is not as effective as gaseous sterilization, it is appropriate in conditions where a low level of contamination is present.
Different liquid chemicals used for liquid sterilization includes the following:
i. Hydrogen peroxide
Hydrogen peroxide is a liquid chemical sterilizing agent which is a strong oxidant and can destroy a wide range of microorganisms.
It is useful in the sterilization of heat or temperature-sensitive equipment like endoscopes. In medical applications, a higher concentration (35-90%) is used.
H2O2 has a short sterilization cycle time as these cycles are as short as 28 minutes where ethylene oxide has cycles that as long as 10-12 hours.
However, hydrogen peroxide has drawbacks like low material compatibility, lower capacity of penetration, and associated health risks.
Vaporized hydrogen peroxide is used to sterilize largely enclosed and sealed areas, such as entire rooms and aircraft interiors.
ii. Glutaraldehyde
Glutaraldehyde is an accepted liquid sterilizing agent which requires comparatively long immersion time. For the removal of all spores, it requires as long as 22 hours of immersion time.