Why is 70% the More Effective Concentration of Isopropyl Alcohol for Disinfection?

What is Isopropyl Alcohol (IPA) and How is it Used?

  • 70% Isopropyl Alcohol is most frequent and commonly used disinfectant in pharmaceutics, hospitals, cleanrooms, and electronics or medical device manufacture is isopropyl alcohol (2-propanol), sometimes known as isopropanol or IPA.


  1. Molecular Weight: 60.10 g/mol
  2. IUPAC Name: Propan-2-ol (C3H8O)
  3. Chemical Formula: CH3CH(OH)CH3
Isopropanol or IPA or 2-propanol

Why is 70% the More Effective Concentration of Isopropyl Alcohol for Disinfection?

  • Isopropyl alcohol (IPA) is fast antimicrobial against bacteria, fungi, and viruses in solutions containing 60 to 90 percent alcohol and 10 to 40 percent filtered water.
  • Once alcohol concentrations drop below 50%, usefulness for disinfection drops sharply. When alcohol concentrations fall below 50%, disinfection effectiveness & activity go down sharply.
  • Remarkably, increased alcohol concentrations do not result in improved bactericidal, virucidal, or fungicidal characteristics.
  • Water in IPA is a vital factor in abolishing or inhibiting the development of pathogenic microorganisms with isopropyl alcohol (IPA).
  • Water is a catalyst that aids in the denaturation of proteins in vegetative cell membranes. 70% IPA solutions penetrate the cell wall more thoroughly, permeating the entire cell, coagulating all proteins, and killing the microbe.
  • Evaporation is slowed by the extra water content, which increases surface contact duration and efficacy. Concentrations of isopropyl alcohol exceed the 91% concentration.
  • As a result, a protective barrier forms, shielding other proteins from further coagulation.


  • Lowering the concentration of IPA may affect the cost.
  • Increase the contact time of IPA.
  • Surface protein coagulation occurs at a slower rate, allowing the alcohol to enter the cell.
  • Presence of water, use in the denaturing process of proteins.
  • Because the concentrations of water and alcohol on either side of the cell wall are different, 70 percent alcohol enters the cell and denatures both enzymatic and structural proteins. This boosts the antibacterial characteristics’ potency.
  • Water slows down the evaporation of IPA.

How to prepare 70% Isopropyl alcohol (IPA)?

  • Take a 100% concentrated IPA.
  • Dispense 700 mL in the volumetric flask.
  • Measure the 300 mL purified Water and add in the volumetric flask to make 1000 mL 70% IPA.

Ref. Guideline for Disinfection and Sterilization in Healthcare Facilities.

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