70% ethanol in tap water... - (Apr/14/2012 )

I'm sorry.. I'm really a noob for cell culture. Just wondering if I can prepare the 70% ethanol disinfectant with Tap water, in my college lab.
Thanks

Of course you can. Real question is - should you? Your lab must have distilled, dd, DI or MilliQ water source - better use one of those. If for some mysterious reason you can't do this - autoclave your water first. If you can't autoclave - at least boil it.

K.B. on Sat Apr 14 07:56:00 2012 said:

Why should you boil the water?
Tap water should be pretty clean, so I imagine you wan to boil it to remove other componets?

And why should you, in the first place, use dd, DI or milliQ water? Whats wrong with tapwater?

Nothing is wrong with it if you want to drink it. But if you want to use it for cleaning in a lab, you should use something moleculary clean.
Also there is small amount of bacteria in tap water, that would probably be severely scavenged by the ethanol, but do you want to use the ethanol to primary desinfect the surfaces in lab or to desinfect the water you put in it?
And of course spraying around liquid with parts of dead bacteria.. nothing I would want to have in my hood.

lyok on Sat Apr 14 08:59:03 2012 said:

Whoa... You work in the lab and you seriously ask this kind of questions?... *facepalm*

K.B. on Sat Apr 14 11:13:14 2012 said:

I do not see what it is wrong with that question.

Deionized water (demineralized water) is not bacteria free... Its not sterile water...
Same goes for dd water.
The changes to get bacteria in it are even higher since people use the same containers over and over and they are not sterile at all!
Even MQ water can contain bacteria.

I do not know from what country you are, but in my country, tap water is pretty clean.

So the question remains: why boil the water the tap water for the 70% ethanol solution and not, for example, boil the di water?

Also: if you boil the water: the dead bacteria will stay in it.. so you dont remove it, so dont see the point trof made since in di water there are bacteria present too.

PS. the standards for tap water (CFU) in many countries is more strict then those for purified water (often no regulation to CFUs at all)

There is most likely a reason why not to use tap water, but your explenation isnt 100% accurate.

So, not sure whether your *facepalm* should be repeated....


(I am strictly speaking of cleaing a bench, not speaking about using the water for other purposes, ddwater etc has its purpose, but not sure why you need to use it for a 70% ethanol solution.. It has to do with the non bacterial susbtances in the water I think, rather then the bacterial ones)

Oh yeah, and I forget to tell: in the ion-exchange units used to make demineralized water, you often have growth of algaes... not that clean either...

another worry with tap water is (at least if the water hardness is high enough, i.e. sufficient Ca²⁺ and Mg²⁺ concentration) that it will precipitate when adding ethanol and you have a fine grained precipitate in the ethanol solution (in our lab it happened after someone did it, because for the non-molecular part he thought it's okay).
And I agree you rarely find water free of everything (and especially in usual demin. water, where bacteria and algae grow after some time) and the spray- and squirt-bottles are not autoclaved, when you fill it with sterile ddwater). Anyway I think the amount is less than in usual tap water and most/all is dead after sufficient time in the ethanol.

And the few dead bacteria and their DNA respectively that are sprayed with any of the waters in the hood should be finished with the UV finally .

I do not know from what lab you are, but in my lab MiliQ water doesn't contain bacteria. At least not at the point leaving the machine.

Trof on Sat Apr 14 15:14:55 2012 said:

MQ is indeed the most pure form of water, but I do not know a lot of labs where they prepare ethanol 70% with MQ.
Do you really make ethanol solutions with MQ? Very very very expensive.