Re: [DIYbio] Re: Transformation questions

> A professor I met told me you can't autoclave CaCl2 ...??
>
> Sounds strange to me because it's a salt... Does it dissociate??
> Anyone heard of this? Maybe it's common knowledge which I didn't have yet...
>
> She told me that you just filter the cacl2 (and showed me where the filters
> are in case I want to use 'em) and bactreria are filthered out by this
> filters.

The dissolution of CaCl2 in water is highly exothermic, so it's
possible to precipitate CaCl2 by heating. But in practice I have
never had any problem with autoclaving CaCl2 by itself. I do it all
the time for making competent cells. But I think if the concentration
is high enough you can get precipitation.

Although, if you are mixing CaCl2 with growth media, you definitely
have to mix the CaCl2 into the media *after* autoclaving. I just
autoclave the two separately, then mix the two solutions in sterile
conditions after the solutions have cooled. For some reason stuff
precipitates in media/CaCl2 mixtures when heated, I'm not sure what it
is though.

Some other things you should not autoclave:
- Detergents
- Sugars (Sometimes this works OK, sucrose is usually fine, but I
filter sterilize just to be safe)
- Sugars with amino acids (Maillard reaction)
- Phosphates with metals

-cory

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