Related to this, I made up citrate buffer at 10x concentration one time, making it 100mM instead of 10mM. I didn't pH the 10x stock, but left it at around pH 2-3. Then, I figured it would save me time and effort to just dilute 100 mls of the stock with 900 mls of water, and pH to 6.0. Well, within about a week or two, there was tons of junk growing in my buffer stock solution, which I had never seen grow in the 10mM buffer. I kept the stock 10x buffer at room temp, which is where I keep the 10mM buffer also. So, I went back to making it up like I used to, 10mM pH 6.0, making 2 liters at a time. i have no idea why stuff would grow in the 10x stock, but not in the working 10mM buffer. Just thought I'd relay that story and see what folks thought about it.
Joyce Kotzuk, UNM pathology

>>> "Nicola  Falconer" <njfja@njfja.screaming.net> 04/26/00 12:22PM >>>
dear Louise and all

Another late reply! We make citrate buffer in 10 litre amounts and it keeps
OK at room temp for a couple of weeks. We use the working stuff for 1 week
topping up as required, so it probably gets changed evry other day.

For measuring ph of buffers, maybe I'm paranoid, but we use a real pH meter,
no diddly stick ones, calbrated weekly, and measure the pH when making the
buffers up. We check our TBS for diluting antibodies EVERY day with above
meter.

For those who use other methods, if it ain't broke don't fix it, BUT if you
have problems with consistancy, guess what I recommend you check first.

regards
John Auld
Immunocytochemistry
Royal Free Hospital
London
UK