Where can I buy 99% isopropyl alcohol?

[Axtman]

I have casually looked at a drug store and grocery store but all I can find is 91% and 70% isopropyl alcohol. Do I have to buy 99% IPA over the net?

[magic]

You could try hardware store, electronics/maker/DIY shops if there are any, maybe computer stores (it's used to remove old thermal greases), chemical suppliers, ...

[georges80]

Unlikely you'll find 99% (or better) at a drug store etc.

I have an electronics supplier (Anchor Electronics, Silicon Valley), where I can buy the MG chemicals 99.9 off the shelf.

If you have no such place locally, then yeah, just order it.

https://www.amazon.com/MG-Chemicals-824-1L-Isopropyl-Alcohol/dp/B005DNQX3C isn't crazy marked up.

cheers,
george.

[testpoint1]

I have casually looked at a drug store and grocery store but all I can find is 91% and 70% isopropyl alcohol. Do I have to buy 99% IPA over the net?

you can buy it from Ebay, much more, 99%

[alpher]

Costco.

[mariush]

Search for 97% or better.

70% is for washing hands, kills stuff better than other concentrations.

Veterinarians also stock isopropyl alcohol, but I wouldn't know the concentration. It's often used with horses so you can ask vet places, pharmacies, if you have no luck in other places.

Acetone is also a very good solvent, which could be used instead of isopropyl alcohol. Just avoid pouring acetone over some plastics  (ex capacitor sleeves) or over printed text - the acetone can take the ink out.

[IanB]

I have casually looked at a drug store and grocery store but all I can find is 91% and 70% isopropyl alcohol. Do I have to buy 99% IPA over the net?

I used to get the MG Chemicals brand from Fry's, but since they went out of business I have no retail options left that I know of. You probably have to order it online if you don't have any electronics stores near you that would be similar to Fry's.

On the other hand, the 91% version might be perfectly fine for cleaning. The IPA will be good for grease and flux, and the water content would help to dissolve salts and other water-soluble things such as flux additives.

[helius]

99.9% isopropyl is for cleaning optical and magnetic assemblies. It is not especially good as a flux remover (due to the ionic contaminants issue mentioned by IanB) and has particular problems with no-clean flux residues.

[jpanhalt]

99.9% isopropyl is for cleaning optical and magnetic assemblies. It is not especially good as a flux remover (due to the ionic contaminants issue mentioned by IanB) and has particular problems with no-clean flux residues.

Do you have a problem with the decimal place? IanB suggested 91%.

[Axtman]

I will be using the 99% IPA to clean the flux, and other contaminants, from circuit boards and switch contacts. I belive Fluke and Tektronix recommend this procedure.

I have used drugstore 91% IPA but found that it left a white residue after the alcohol evaporated. I then had to clean the white residue with distilled water. I am hoping with the 99% IPA that I can skip that step.

[jpanhalt]

Why do you think 99% IPA will be better than 91% at dissolving "salts?"  That's illogical.

[edfarrington93]

I read that the difference between them is water content. 99% being the purest you can get, it evaporates the fastest and is good for electronics since there is basically no water. 70% kills germs better because the higher water content keeps the alcohol on the target surface longer allowing the alcohol time to kill the germs, whereas 99% is basically useless for germs because it doesn't remain on the surface long enough.

[mariush]

It's not about how long is stays, it's making it possible for the alcohol to enter cell walls and damage them, easier.

See https://munglobal.com.au/resources/knowledge-base/pathogens/why-70-isopropyl-alcohol-is-a-better-disinfectant-than-99-isopropyl-alcohol/

quoting from it

70% isopropyl alcohol kills organisms by denaturing their proteins and dissolving their lipids and is effective against most bacteria, fungi and many viruses, but is ineffective against bacterial spores (CDC, 2020).

Use of the more concentrated solutions (99%) will result in almost immediate coagulation of surface or cell wall proteins and prevent passage of the alcohol into the cell. When the outer membrane is coagulated, it protects the virus or bacteria from letting through the isopropyl (Widmer and Frei, 2011). Thus the stronger solution of isopropyl is creating a protection for the germ from the antiseptic properties of isopropyl, rendering the virus or bacteria more resilient against the isopropyl alcohol. To put it simply, higher concentrations cause an external injury that forms a protective wall and shields the organism. Furthermore, 99% isopropanol evaporates very quickly which does not allow it to penetrate cell walls and kill bacteria, and therefore isn’t as good for disinfecting surfaces. In other words, it breaks down the outside of the cell before it can penetrate the pathogen.

In comparison, a 70% isopropyl alcohol can effectiveness cross over the cell membrane, thereby attacking the entire cell and killing the bacteria (CDC, 2020). The benefits of using 70% alcohol are

    Coagulation of surface proteins proceeds at a slower pace, thereby allowing the alcohol to enter the cell.
    70% alcohol, being a dilution of absolute alcohol, contains water which is essential in the denaturing process of proteins.
    Due to the concentration difference of water and alcohol on either side of the cell wall, 70% alcohol enters the cell to denature both enzymatic and structural proteins. This increases the potency of its antimicrobial properties.

The CDC recommends 70% for disinfecting one’s household and routine cleaning (CDC, 2020)

[helius]

"Good for electronics"... most circuit boards manufactured today undergo aqueous cleaning. For specific components such as photoarrays, fiber optic launchers, or CdS sensors, avoiding water spots is very important (that's why I mentioned optical assemblies). For most electronics this doesn't matter at all, the only thing that matters is proper cleaning technique and a solvent strong enough to dissolve all residues. 91% isopropyl (the remainder is water) has acceptable performance on non-activated rosin flux. For most activated fluxes used today a stronger solvent mixture is desired, which can be achieved using a combination of alcohols, alkanes, ketones and esters. When formulated correctly the mixture remains plastic and soldermask safe.

[BrokenYugo]

IIRC 99% turns to 91% quickly by picking up atmospheric water. Keeping alcohol "dry" is tricky.

The white stuff (tin and lead oxides I think?) isn't terribly soluble in anything, solutions to the problem generally involve commercial purpose made flux removers, changing flux/solder, or simply leaving the rosin on the board.

[Nusa]

There's a tradeoff between drying time and cleaning power. Higher concentrations dry faster, lower concentrations often clean better because there's more soak time.

And yeah, it's hard to keep 99% stuff from absorbing moisture from the air unless you're religious about keeping the cap on tight. Plus you paid a lot more for that concentration.

[jpanhalt]

IIRC 99% turns to 91% quickly by picking up atmospheric water. Keeping alcohol "dry" is tricky.

The white stuff (tin and lead oxides I think?) isn't terribly soluble in anything, solutions to the problem generally involve commercial purpose made flux removers, changing flux/solder, or simply leaving the rosin on the board.

Here's Kester's study of the "white stuff:"  https://www.kester.com/Portals/0/Documents/FAQs/White_Residue.pdf

Without more information (e.g., solder, flux, aging), it is speculative what the residue is.

[Axtman]

Only on the EEVblog forums can you ask a question about electronics and get medical advice! 

Thanks guys for your input.

[IanB]

I have used drugstore 91% IPA but found that it left a white residue after the alcohol evaporated. I then had to clean the white residue with distilled water. I am hoping with the 99% IPA that I can skip that step.

It doesn't matter what concentration you use if you let the solvent evaporate, since once the solvent evaporates it will leave behind anything that was dissolved in it.

The key to effective cleaning is to rinse properly. Rinsing carries away dirt and contaminants leaving clean surfaces behind. If you don't rinse, you have not removed the dirt. (The same applies when washing hands, clothes, dishes, cars, and most anything else.)

[Axtman]

I have been using 91% IPA in a spray bottle. It works well if I need clean a whole board and don't want to soak or pour the IPA. I can spray a small area if I am careful. For really small areas I use a Q-tip soaked in IPA.

https://www.riteaid.com/shop/ra-trggrspry-alchl-91-10z-0358266

[Jeroen3]

Not all contaminants dissolve in alcohol, and not all dissolve in water.
It has something to with polar molecules and stuff. I'm no chemist, he is:
 

70% works best for typical cleaning and degreasing, just get that.

[ve7xen]

Does anyone know what the reason is for the lack of availability of 99% in so many places? Pretty much any drug store here carries it for cheap (like < $5 for 500ml) and it's easy to find. Even the local grocery store (which does not have a pharmacy) was carrying it at the beginning of the pandemic alongside the 70%, though not sure if they've kept that up. Is there some sort of regulation or what?

[Kleinstein]

One rarely needs the 99% pure IPA. When used in normal humdity air, it will capture water quite fast while using it on the PCB.

Purity can still be important, but it is not about the water, but about other part in there. Some are bad (e.g. hardly soluble parts, like platicizer deissolved from the bottle, traces of silicone) and some don't really matter (e.g. water or ethanol) for the more normal cleaning jobs.  99.9% IPA with 0.1% silicone is pretty ugly. 90% IPA with 10% water could be pretty good.

[notsob]

Try looking for a dedicated supplier, like this one in AUS

https://www.sydneysolvents.com.au/

[Bassman59]

I have casually looked at a drug store and grocery store but all I can find is 91% and 70% isopropyl alcohol. Do I have to buy 99% IPA over the net?

In the US? The local Ace Hardware stores should carry it.