The World Health Organization (WHO) has published recipes for liquid handrubs. In both recipes the main ingredient (75% or more) is alcohol. This may be ethanol or isopropanol (which I discussed in A is for Alcohol). It only contains two other ingredients. Hydrogen peroxide is an antimicrobial agent. A small quantity of glycerol is acts as a wetting agent.
This recipe is based on a WHO recipe. It adds peppermint oil to soften the smell of alcohol.
Hydrogen peroxide is corrosive when undiluted. Please read the handling instructions that should be provided when you buy it. Be careful not to get it on your skin, and wash it off under cold running water immediately if any does touch your skin. Rinse out containers used for measuring. Rinse them out several times with fresh water.
There appears to be a consensus that an effective hand sanitizer should contain a minimum of 60% alcohol and a maximum of around 95%. There should be some water in the formulation. The water helps the alcohol to penetrate the outer layer of a virus. Once the outer layer has been penetrated, the alcohol disrupts and destroys what is left. One study tested the efficacy of a number of hand sanitizer formulations with alcohol ranging from 60% to 95%. It identified two formulations containing 70% as the most effective amongst those tested (so increasing the alcohol content above 70% doesn’t guarantee a more effective sanitizer).
In order to produce a sanitizer that contains 70% alcohol, you have to start with alcohol at a higher concentration (because everything else in the formulation will reduce the proportion of alcohol). This recipe uses Isopropyl alcohol at a concentration of 99.8%, and produces a sanitizer with a 70% alcohol content.
Ingredients
-
- 350 ml Isopropyl alcohol 99.8%
- 110 ml boiled and cooled water
- 5 ml Hydrogen peroxide 12 vol
- 35 ml Vegetable glycerine
- 0.5 ml Peppermint essential oil
Method
Pour the glycerine into a clean bottle that will hold 500ml or more liquid. Add the boiled water and shake. Carefully add the hydrogen peroxide, and shake again.
Measure the alcohol by volume and add it to the other ingredients. The other ingredients have a density of about 1 gramme per 1 ml, so you can safely weigh them on the assumption that the result will be accurate enough. Isopropyl alcohol has a density of 0.786 grammes per 1 ml, so you will add roughly 25% more alcohol than you intend if you weigh it without making a correction.
Add the peppermint oil. Shake the bottle to mix
Label the bottle(s) with the contents. Add labels to the effect that the mixture is flammable, toxic if ingested, and you should avoid getting it in your eyes.
