# Topical hand sanitizer production question from tutor; Concentration and dilution of chemicals of known concentrations [closed]

The question is as follows:

You are in charge of making hand sanitiser based on the WHO Guide to handrub formulations,

FORMULATION 1 Final concentrations: • Ethanol 80% (v/v), • Glycerol 1.45% (v/v), • Hydrogen peroxide 0.125% (v/v)

You are given; Ethanol @94.45% ABV

H2O2 @6% concentration

Glycerin @100% concentration

Water

Using 10,000L of ethanol @94.45%, what volume of (a)glycerin and (b)H2O2 are needed to achieve the final concentration in FORMULA 1? What would the volume of H2O2 be if given a 3% concentration solution? (c)What volume of water is needed to be added?

The following is my attempt;

Batch production For 100ml 100*80 = 8000 / 94.45 = 84.7008999ml

For 1L Batch 847.008999ml = 0.847008999L

Have 10,000L @94.45% ABV 10000L / 0.847008999L = 11806.25L Total hand san made at 80% v/v ethanol

If 10000L ethanol @ 94.45% then 1806.25L used for dilution between H2O2, glycerine, and water

(a) glycerine @100% conc 1.45% v/v Glycerine 11806.25L / 100 = 118.0625 X 1.45 = 171.19L

(b) H2O2 @3% 11806.25L / 100 = 118.0625 X 0.125 = 14.78L

14.78L / 3 = 4.919 X 100 = 491.93L

If have 6% conc H2O2 14.78 / 6 = 2.459 X 100 = 245.96L

(c) 1806.25 – 171.19 – 491.93 = 1143.13L water

Am a bit unsure if correct, especially with part (b) H2O2, Thanks in advance!

• The formulation is given by amount / volumes to be mixed. Forget final % concentration. To get exactly the same result (which might be overshooting but I am not here for medical advice) just makes conversion on the ingredients side. Proportions also. This is because volume is not addictive. H2O2 in particular could be omitted. It serves to destroy spores eventually in water. A health organisation cannot give non perfect recipes. That is a multi purpose sanitizer to be deployed in every scenario. – Alchimista Mar 28 at 6:43

Yes, I agree in the technical proportions, and here is another web reference with a topical solution prep starting with 96% Ethanol (which may be of interest to you and others).

As a side comment, however, there is only economic loss involved by substituting a higher % H2O2 (if you are interested in a potentially more powerful mix) for your personal use. Supporting comments from Wikipedia:

Hydrogen peroxide may be used for the sterilization of various surfaces,[64] including surgical tools,[65] and may be deployed as a vapour (VHP) for room sterilization.[66] H2O2 demonstrates broad-spectrum efficacy against viruses, bacteria, yeasts, and bacterial spores.[67] In general, greater activity is seen against Gram-positive than Gram-negative bacteria; however, the presence of catalase or other peroxidases in these organisms may increase tolerance in the presence of lower concentrations.[68] Higher concentrations of H2O2 (10 to 30%) and longer contact times are required for sporicidal activity.[69]

where the key takeaway for me is that even with 10% to 30% H2O2, longer contact times can be required for select conditions.

Also, there may be possibly a harsher effect on one's skin, but from a marketing perspective, the hydrogen peroxide boost may be a plus.

If for personal use only, a less convenient option to consider, in my opinion, is not adding the 'distilled water component' until the time of point-of-use in quantities needed. I would consider substituting for distilled water inexpensive raw 'tap water'. This will likely reduce shelf-life and the stability of the H2O2, which could result in the problematic liberation oxygen in the dispensing container. Possibly offsetting, in my view, is the introduction of favorable transition metals salts.

Possibly chemistry with ferrous ions that may be present, for example, which could engage in a Fenton reaction (web link to 'A convenient lecture demonstration of the Fenton reaction is presented with references to applications in medicine and environmental engineering') associated with the creation of powerful hydroxyl radicals (capable of breaking down organic compounds). Unfortunately, this usually requires more acidic pH (in the current context, from say further adding citric acid). Tap water may also contain manganese, cuprous,..., ions, which could also engage in related Fenton-type reactions (with radical products). Interestingly, with copper ions, for example, this usually occurs closer to more neutral pH conditions.