Chemical Methods of Sterilization and Disinfection

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 8C). 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 irritatesmucosa; skin contactmay result in
inflammations or allergic eczemas. Formaldehyde is a broad-spectrum ger-
micide 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 formal-
dehyde is based on protein denaturation.
Another aldehyde used for disinfection purposes is glutaraldehyde.

Alcohols. The types of alcohol used in disinfection are ethanol (80%), propanol
(60%), and isopropanol (70%). Alcohols are quite effective against bacteria and
fungi, less so against viruses. They do not kill bacterial spores. Due to their
rapid action and good skin penetration, the main areas of application of al-
cohols are surgical and hygienic disinfection of the skin and hands. One dis-
advantage is that their effect is not long-lasting (no depot effect). Alcohols
denature proteins.

Phenols. Lister was the first to use phenol (carbolic acid) in medical applica-
tions. Today, phenol derivatives substituted with organic groups and/or halo-
gens (alkylated, arylated, and halogenated phenols), are widely used. One
common feature of phenolic substances is their weak performance against
spores and viruses. Phenols denature proteins. They bind to organicmaterials
to a moderate degree only, making them suitable for disinfection of excreted

Halogens. Chlorine, iodine, and derivatives of these halogens are suitable for
use as disinfectants. Chlorine and iodine show a generalized microbicidal ef-
fect and also kill spores.
Chlorine denatures proteins by binding to free amino groups; hypochlo-
rous acid (HOCl), on the other hand, is produced in aqueous solutions, then

disintegrates into HCl and 1/2 O2 and thus acts as a powerful oxidant. Chlorine
is used to disinfect drinkingwater and swimming-poolwater (up to 0.5mg/l).
Calcium hypochlorite (chlorinated lime) can be used in nonspecific disinfec-
tion of excretions. Chloramines are organic chlorine compounds that split off
chlorine in aqueous solutions. They are used in cleaning and washing pro-
ducts and to disinfect excretions.
Iodine has qualities similar to those of chlorine. Themost important iodine
preparations are the solutions of iodine and potassiumiodide in alcohol (tinc-
ture of iodine) used to disinfect skin and small wounds. Iodophores are com-
plexes of iodine and surfactants (e.g., polyvinyl pyrrolidone). While iodo-
phores are less irritant to the skin than pure iodine, they are also less effective
as germicides.

Oxidants. This group includes ozone, hydrogen peroxide, potassiumperman-
ganate, and peracetic acid. Their relevant chemical activity is based on the
splitting off of oxygen. Most are used as mild antiseptics to disinfect mucosa,
skin, or wounds.

Surfactants. These substances (also known as surface-active agents, tensides,
or detergents) include anionic, cationic, amphoteric, and nonionic detergent
compounds, of which the cationic and amphoteric types are the most effec-
tive (Fig. 1.8).
The bactericidal effect of these substances is onlymoderate. They have no
effect at all on tuberculosis bacteria (with the exception of amphotensides),
spores, or nonencapsulated viruses. Their efficacy is good against Gram-pos-
itive bacteria, but less so against Gram-negative rods. Their advantages in-
clude low toxicity levels, lack of odor, good skin tolerance, and a cleaning ef-


10 Responses

  1. Very great description of Chemical methods of sterilization. I like it.

  2. The stirrup bone, in the ear is the smallest.

    The femur, between the knee and the thigh, is the largest.
    is this true?

  3. the name of the smallest bone is stapes, one of the three ear bones. and ya, the largest is femur.

  4. hi ankit, i dont think its a science question blog.find this blog when i was seraching abt hardwar,and one more thing your your trip mussorie-landour is very good scripted on net keep it up and dushyant keep writing abt new invention and their effrect on human live style.
    keep blogging guys

    with best regards

  5. I have been busy in my exams and they are still in my pursuit. I will post new topics as soon as I get free from exams. And thanks Neha

    • i have some study matri and want to share with you and, also ned ur comment too. so please share when u get free frm exam.


  6. I will be more than happy to see that material Neha. and I will get free on 18th January.

  7. other chemica disinfectants are:
    heavy metals
    soaps and detagents
    oxidising agents

  8. Am very for this wonderful idea.

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