Help: Concentration units and dilutions - For Morph (or anyone who is knowledgeable about Chemistry)

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Help: Concentration units and dilutions - For Morph (or anyone who is knowledgeable about Chemistry)

Post by Green » September 10th, 2020, 10:43 pm

I'm diluting a stock solution of a disinfecting product into distilled H20. I cannot figure out what the percentages listed on products actually mean...

I assumed it was in terms of V/V.

If so, I could use (C1)(V1) = (C2)(V2). And it would be straight forward.

I checked some MSDS sheets, and they don't list any units for the concentrations.

So I'm wondering if they could be using W/W or W/V.

Really hoping I won't need complex calculations invoking molar mass, etc. But it's ok if I do, as long as I won't need special equipment beyond the graduated cylinders and stirring rods I bought.

Thanks!

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MorpheusPA
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Re: Help: Concentration units and dilutions - For Morph (or anyone who is knowledgeable about Chemistry)

Post by MorpheusPA » September 11th, 2020, 2:28 pm

You're going to need to be a lot more specific. :-) What's going into what and what are you trying to do? Is this to clean the shower and kitchen, or to disinfect a formal laboratory situation to government standards?

Good news, however, for most home-based disinfecting products, it doesn't much matter. When we say 1:50 bleach, we mean V/V. 1 tsp bleach to 50 tsp water. Or 1 ounce to 50 ounces.

Thereabouts. It doesn't much matter, really. 1 to 52 will still kill pretty much all bacteria and viruses. For my shower cleaner, I just wing it, really.

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Re: Help: Concentration units and dilutions - For Morph (or anyone who is knowledgeable about Chemistry)

Post by Green » September 11th, 2020, 9:56 pm

MorpheusPA wrote:
September 11th, 2020, 2:28 pm
You're going to need to be a lot more specific. :-)
Ok, I'm dealing with QUATs. (Making my own disinfecting wipes.)

The Clorox brand wipes state 0.184% of both Benalkonium Chloride and Dimethyl Ethylbenzyl Ammonium Chloride.
But I'm not sure if that's per volume...?

I have stock solution that is 10% in both (Bet you're familiar with the product I have based on what I said here. But shhh, don't tell anyone because there will be a run on the product if everyone finds out what it is!) Planning to dilute with distilled H20. If it's V/V, I can use the formula I mentioned (concentration 1 times volume 1 equals concentration 2 times volume 2), and pick an arbitrary but decent number for the diluted volume. Then solve for the other volume.

However if it's not V/V...

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Re: Help: Concentration units and dilutions - For Morph (or anyone who is knowledgeable about Chemistry)

Post by MorpheusPA » September 12th, 2020, 1:48 am

Gotcha. And yes, BTDT, except in terms of hand sanitizer. V/V. I'm presuming you mean Benzalkonium Chloride, though.

And again, this is not an exact science, although I don't recommend overexposure to DEAC. Not that it'll be a problem, some lab-grade stuff goes to 0.4% (but you are supposed to wear gloves). Aerosols and vapor is not a problem--but exercise care with the lower dilution solutions you have, of course.

One thing to note is that the CDC does not state that benzalkonium chloride reliably kills COVID-19 (quite the opposite, actually). May I recommend ethanol as well?

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Re: Help: Concentration units and dilutions - For Morph (or anyone who is knowledgeable about Chemistry)

Post by Green » September 13th, 2020, 10:50 pm

MorpheusPA wrote:
September 12th, 2020, 1:48 am
One thing to note is that the CDC does not state that benzalkonium chloride reliably kills COVID-19 (quite the opposite, actually). May I recommend ethanol as well?
That's interesting...but I'm targeting making an exact replica of the pre-made wipes that everyone has been using. It does list human coronaviruses on it, though I think only the cold-causing ones were tested. Then again, if everyone has been these wipes on their surfaces, and people aren't getting sick from those surfaces, then it must be working (when used properly...but who leaves the surface wet for 4 min when you reuse a wipe over a larger area and the amount of disinfectant diminishes over time?) In any case, I trust the original product does something, and just want to make as exact a version as I can. So, I sourced the stock solution, the special wipes that don't' degrade, etc.

In summary since you said it's V/V, do you feel I'm good using the (C1)(V1) = (C2)(V2) equation, and targeting the 0.184% of the original product when I dilute with my distilled water? I'm thinking of picking a reasonable number for V2, like 1 cup. It'll be a little trial and error, though. I need enough volume to wet the wipes but not so much to be wasteful.

Speaking of which, now that you confirmed it's V/V (*how did you know that, btw? I've taken 5 different chemistry classes in college, and I still couldn't figure it out!), I will say I'm glad that my pint of 10% disinfectant will be enough to make an insane number of batches...far more that I should need to, and will outlast the quantity of QUAT-compatible wipes I bought. Not to mention, the pre-made wipes are beginning to become available in drips and drabs again.

Thanks again, and I really enjoy your posts.


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Re: Help: Concentration units and dilutions - For Morph (or anyone who is knowledgeable about Chemistry)

Post by MorpheusPA » September 14th, 2020, 3:21 am

It's the DEAC, which is listed for coronavirus. And I know V/V as I've done this before and had to do my own research; it's in the instructions online for making this kind of thing. Except I was doing hand sanitizer and still make some random hand creams when I have the time and inclination. Preservatives and disinfectants are always V/V unless specifically otherwise stated.

(I did just make the soap for some laundry detergent as I'm on my last pound, which is mass/mass, but I seriously just eyeball that and I came up with my own formula anyway. Six pounds of homemade Stain Formula soap grated fine, four pounds of sodium carbonate, two pounds of borax. Give or take. If I'm off half a pound on anything, it doesn't matter. 1 Tbsp per load, one batch lasts three years. Costs jack crap per load compared to commercial detergents and works better).

Given the natural variance in percentage dilutions (seriously, if you look up BAC and DEAC in use, you'll find a very wide variance in percentages), C1/V1 = C2/V2 should be just fine. There's a recursive set of formulae for multiple dilutions that works better, but that's overly complex and, again, really unnecessary here. Whether you hit 0.184 or slide a bit and hit 0.2%, you're quite close enough and commercially available wipes do have that much variance and more from what a bit of spot research showed.

One cup should be...an awful lot of wipes. I've never done it, so I don't know the saturation levels...but a spot of online research shows that 1 cup of water can dampen a small roll of paper towels such as would be cut down to fit into a coffee can well enough to use as wipes. Which is a very clever idea.

Around here, we've solved the coronavirus conundrum by isolating ourselves quite thoroughly. On the days when my mental state breaks, I go into the basement and build forts out of canned peas and rolls of toilet paper. :-) But since we both expect all heck to break loose again when the normal flu season restarts in October/November, better safe than sorry, I suppose. Not that heck ever really stopped breaking loose.

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