CDC recommends at least 60% alcohol in hand sanitizer.
To combat coronavirus disease COVID-19 pandemic, WHO has recommended 2 formulations which meet both ATSM (US) and EN (European) standards. Although the formulations are intended for individual health-care facility, anyone with basic laboratory apparatus like beakers, graduated cylinders, funnels etc can produce the hand sanitizers.
While WHO recommended active ingredients are available locally, the alcohol content may not be as high as the formulations. Fortunately, active ingredients with at least 60% alcohol are also accepted by CDC, we can use this guideline to produce effective hand sanitizers.
Once we learn how to adjust the solution volume to meet CDC acceptance, we can become self sufficient in making our very own alcohol hand sanitizers.
Alcohol Volume Adjustment for Effective Hand Sanitizer
Both WHO’s formulation 1 and 2 are designed for producing 10 L of alcohol hand sanitizers. However, the same alcohol concentration may not be available locally. We can adjust the ingredient volume with simple formulas as shown below.
WHO Formulation 2
Let’s use WHO formulation 2 for illustration purpose.
- Isopropyl alcohol 99.8%
- Hydrogen peroxide 3%
- Glycerol 98%
- Sterile distilled water (preferred) or boiled cold water (free of visible particles)
Final Product (10 L):
- Isopropyl alcohol 75% (v/v) (7515 ml)
- Hydrogen peroxide 0.125% (v/v) (417 ml)
- Glycerol 1.45% (v/v) (145 ml)
- Sterile distilled water or boiled cold water (1923 ml)
- Refer to homemade alcohol hand sanitizer with WHO formulations for more details.
- It’s advisable to buy active ingredients locally due to high import duty for alcohol, and legal requirements by local authority.
The formulas for calculating the ingredient volumes are:
Raw ingredient volume (ml) = final ingredient concentration (% in v/v) / raw ingredient concentration (%) x final total volume (ml)
Water volume (ml) = final total volume (ml) – (total volume of all ingredients)
Apply above formulas to WHO formulation 2:
Isopropyl alcohol volume = 75 / 99.8 x 10000 = 7515 ml
Hydrogen peroxide volume = 0.125 / 3 x 10000 = 417 ml
Glycerol volume = 1.45 / 98 x 10000 = 148 ml
Sterile distilled water volume = 10000 – (7515 + 417 + 148) = 1920 ml
The calculated volumes are consistent with the volumes in WHO formulation 2 except that glycerol volume is 3 ml more. One possible explanation is that glycerol concentration used in WHO formulation has not been updated to 100% from 98%. This explains why final glycerol volume as 145 ml instead of 148 ml. Nevertheless, this discrepancy is too small to impact the alcohol content in hand sanitizer.
Adjust Ingredient Volume
In the event where alcohol content of local active ingredient is lower than WHO formulation 2, we still can use the local ingredient and adjust the volume as per the formulas shown in previous section.
For instance, local active ingredient is 70% isopropyl alcohol in a 1 L bottle. As such, we won’t be able to achieve the same final product as per WHO formulation 2. However, we can still produce final product of isopropyl alcohol above 60% as recommended by CDC:
Isopropyl alcohol volume = 60 / 70 x 1000 = 857 ml
Hydrogen peroxide volume = 0.125 / 3 x 1000 = 41.7 ml
Glycerol volume = 1.45 / 100 x 10000 = 14.5 ml
Sterile distilled water volume = 1000 – (857 + 41.7 + 14.5) = 86.8 ml
It’s possible that a small amount of isopropyl alcohol may evaporate during the mixing process. Therefore, we may need to add more isopropyl alcohol to make up the loss.
Alternatively, we can increase the alcohol content in hand sanitizer. For example, we can produce hand sanitizer with 65% isopropyl alcohol instead:
Isopropyl alcohol volume = 65 / 70 x 1000 = 929 ml
Sterile distilled water volume = 1000 – (929 + 41.7 + 14.5) = 14.8 ml
Obviously, the lower the alcohol content of active ingredient, the more difficult to achieve target alcohol concentration in the final product. In this scenario, it’s advisable to produce larger volume of hand sanitizer like 5 L or 10 L so that the final ingredient volumes are not too small to manage.
Effectiveness of Hand Sanitizer with Aloe Vera Gel
With the knowledge of adjusting the volume of active ingredients, we can also use it to verify the effectiveness of other do-it-yourself hand sanitizers. Let’s examine one of the most popular do-it-yourself hand sanitizer recipes with aloe vera gel as the humectant. The recipe is 2/3 part of 99% alcohol and 1/3 part of aloe vera gel. Assume that 1 part is equal to 1000 ml:
2/3 part of 99% alcohol = 2/3 x 1000 = 667 ml
The alcohol concentration in the final product is:
Alcohol concentration = 667 / 1000 x 99 = 66%
The calculated percentage above shows that this recipe has achieved alcohol concentration above 60% in the final product. In practice, the final alcohol concentration will be lower than calculated value due to evaporation.
The Most Effective Method to Keep Hands Clean
Regardless of which formulas we use, they’re still not as good as hand washing with normal soap and water. Both WHO and CDC highly recommend simple hand washing as the most effective preventive measure against coronavirus. Use hand sanitizer only when soap and water are not available. This will cut down our reliance on hand sanitizers drastically. Most importantly, soap and water are readily available while working from home! Or ask Alexa the best way for hand hygiene.
Wash hands and be socially responsible.
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