Basseterre, St. Kitts, May 07, 2020 (SKNIS): While appearing on the May 06 National Emergency Operations Center (NEOC) COVID-19 Daily Briefing, Director of the St. Kitts and Nevis Bureau of Standards, Stuart Laplace, provided some clarity surrounding the misconceptions of hand sanitizers.
Mr. Laplace said with respect to the concentration of alcohol persons were asking why using a 91 percent isopropyl alcohol is not as effective as a 70 percent. He said that persons have also been asking why the alcohol percentage has to be between 60 and 70 percent.
“The reason for that is that when you have pure alcohol, let’s say isopropyl alcohol, is one of the alcohols that is heavier than the grain alcohol, which is ethanol. It’s cheaper to make and it has a high vapour pressure. So that means when you place alcohol or 99.8 percent isopropyl strength on your hands, only the point of contact is effective. From the moment you start to move that alcohol around on your hand, it becomes ineffective,” he said.
“The reason for that is that when you add water to alcohol to dilute to between 60 and 70 percent, it increases the strength in terms of the pliability of the alcohol across all areas. That means the water acts as a catalyst to allow the prolonged use of the alcohol to move about on the surfaces that you are trying to sterilize, in this case your hands,” he added.
Mr. Laplace said that in the case of isopropyl, it is ideal because its features allow it to not only clean oils and grease deposits, but it is easy to dissolve in water and has a low vapour pressure compared to its counterparts like methanol and butanol.
The director informed why persons cannot use, for example, 70 percent isopropyl to make their own hand sanitizer.
“You will be diminishing the strength of the alcohol,” he said. “That is why if you are making the sanitizer you have to start somewhere in the 90s for your alcohol. So, when you do your dilution ratio it will bring you down between the 60 to 70 range, which as I have mentioned before increases the contact time between the alcohol and the microbes.”
Mr. Laplace explained the definition of contact time.
“That gives the alcohol enough time to move across the membrane of the cell walls of the bacteria and it takes the alcohol along with it and the nature of the proteins on the inside,” he said.
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