At a 70% concentration, however, the ethanol takes longer to evaporate and this longer contact time means that it is able to penetrate cells more effectively. The water in a 70% grade is also important in denaturing proteins. And 70% ethanol also tends to be cheaper and is less flammable [1].
First, it has been found to be more effective at killing microorganisms than higher concentrations of isopropyl alcohol. This is because the water content in the 70% IPA solution allows for better penetration into the microorganisms and denaturation of proteins.
Why Is 70% the Most Effective Concentration of Denatured Ethanol for Disinfection? Denatured ethanol, particularly in solutions between 60% and 90% alcohol with 10 – 40% purified water, is rapidly antimicrobial against bacteria, fungi, and viruses.
70% Denatured Ethanol for Surfaces and Objects
Ethanol is low-level disinfectant considered highly effective against most common viruses. Clean surfaces, gloves, notebooks, phones, equipment, or any compatible material. Use alcohol with care: may degrade some types of plastics, display surfaces, and enamels.
Since a 70% ethanol solution has more water, it takes longer to dissolve and thus can actually penetrate the bacterial cell wall and kill it.
Even though you may think the higher concentration is more effective, experts say 70% is actually better for disinfecting. It has more water, which helps it to dissolve more slowly, penetrate cells, and kill bacteria. The disinfecting power of rubbing alcohol drops at concentrations higher than 80%-85%.
Ethanol for Disinfection
Ethanol is an effective disinfectant at concentrations between 70% and 90%. Although it may seem counter-intuitive, 70% ethanol seems to be the most effective concentration, as 90% ethanol coagulates the protein, and the protein layer that is created effectively renders the cell dormant.
Alcohols are not recommended for sterilizing medical and surgical materials principally because they lack sporicidal action and they cannot penetrate protein-rich materials.
Glutaraldehyde is considered one of the most effective disinfectants for hospital use.
Solutions of 70% IPA in water should be left on surfaces for 30 seconds to ensure disinfection. Pure (100%) IPA evaporates too quickly for such use and is less effective. - To clean surfaces with soap and water before cleaning with IPA.
Water acts as a catalyst and plays a key role in denaturing the proteins of the cell membrane. At a concentration of 70%, the alcohol-based disinfectant solution penetrates the cell wall more thoroughly, soaking through the entire cell, coagulating all proteins, thereby killing the microorganisms.
Ethanol is bad for cold-starting, because it doesn't burn as quickly as gasoline. (It has a higher octane, if you're interested.) Pure ethanol would be useless as fuel in the winter months. There are no passenger cars designed to take E100 (but some racing cars are) so it could damage your car engine.
70% Ethanol
Aqueous alcohol solutions are not appropriate for surface decontamination because of the evaporative nature of the solution; a contact time of ten minutes or more is necessary and not achievable using a 70% (v/v) aqueous solution of ethanol.
Because higher concentrations tend to evaporate too quickly, and lower concentrations are not strong enough, 70 alcohol is most common. For antiseptics, ethyl is commonly used as it is less harsh on living matter and less likely to cause burns or injuries to the skin.
Alcohols exhibit antimicrobial activity by denaturing and coagulating proteins within the microbial cell wall. Ethanol is also effective against viruses and can be combined with other alcohols to achieve a powerful synergistic effect against various microorganisms.
Mechanisms of Action
The primary mode of action is related to coagulation/denaturation of proteins and solubility of the alcohols in lipids. Without water, coagulation cannot occur, therefore a 70% solution of isopropyl alcohol or ethanol will be more effective than higher concentrations of alcohol.
You can only ever scientifically say that you are able to reduce the microbial load by a proportion of the initial population. This is why most disinfectants sold for domestic use indicate they kill 99.9% of germs.
HOCl, or hypochlorous acid, is a unique molecule effective at killing microbial pathogens. Unlike hypochlorite (OCl–), which is negatively charged, HOCl is neutrally charged, allowing it to easily penetrate the walls of bacteria and destroy them with its strong oxidation potential.
Ethanol concentrations between 60-95% are generally effective, with 80–85% considered optimal [5]. Higher concentrations exhibit reduced potency, while concentrations below 50% are less effective.
DNA is washed with 70% ethanol to remove some (or ideally all) of the salt from the pellet. If water was used as the wash then DNA would dissolve again and if 100% ethanol was used the salt would not wash off because sodium salts are poorly soluble in ethanol.
While the relative effectiveness of alcohol and bleach on bacteria and viruses does not vary greatly, it is important not to mix the two agents during cleaning.
70% Denatured Ethanol solutions are intended to be used for cleaning and residue removal: Cleaning general surfaces. Pre-cleaning before disinfectant application. Removing residues after disinfectant application.
First and foremost, it helps to maintain a clean and sterile environment, particularly in settings where biological or chemical experiments are conducted. Alcohol is a widely used disinfectant due to its ability to kill a broad spectrum of microorganisms, including bacteria and viruses.
While often as effective a disinfectant as bleach, these compounds are also much gentler on fabrics. To sum it up, bleach is one of many chemicals that work as a disinfectant, though one with serious stain removing power, so be mindful of where and when you use it.
Chlorine dioxide is a microbicidal and sporicidal chemical, and it has been proven effective during decontamination of spores without being very harmful to human beings. However, the reported mechanism of action is not consistent in the literature, especially for DNA.