Overshot pH of Competent cell buffer (RbCl) :( - (Jun/09/2008 )

Hi guys, I've got a problem concerning some competent cell buffer I'm using to make a batch of... competent cells. I was trying to make this buffer containing RbCl when I overshot the pH while trying to get it to pH5.8 with acetic acid. The protocol I was using didn't say to use dilute acetic acid, so I just went ahead with glacial acetic acid. One drop, and the pH jumped over 1.0! Now I'm trying to get it to 5.8 (it's at 5.5).

Note that the first time I made up the solution, the PhD student did the same thing (I wasn't there when she put in the glacial acetic acid so I didn't know how much the pH was going to jump from one drop... she messed up my first solution). We tried putting in some KOH to increase the pH, but the solution turned a yellowish tint. Now I'm afraid to try and do the same thing, and I don't know what to do. Arrrgggghhhhhhhh!!

P.S. - RbCl is expensive, so I didn't want to make up a third solution (I'm also kind of lazy, and would prefer not to measure out all the ingredients again).

Here is the recipe for the Competent Cell Buffer 1:

100mM RbCl
50mM MnCl2*4H2O
30mM Potassium acetate
10mM CaCl2*2H2O
15% (w/v) glycerol
Adjust to pH 5.8 with acetic acid (DILUTE)
Sterilize by filtration

Almost forgot to ask the actual question - Is it possible to increase the pH to 5.8 without completely destroying the solution? Has anyone else tried to do this?

Thanks everyone.

One approach would be to make another batch of the solution and mix them until the pH is correct. The problem is that the Mn++ ions precipitate out of solution. We've found that small amounts of the precipitate (which will be filtered out anyway) have little or no effect on the solution.

We've found that the RbCl is not necessary for high efficiency, and use this protocol with better results:
http://openwetware.org/wiki/TOP10_chemically_competent_cells