using sodium hydroxide to adjust pH level of buffer

[jumi08]

I am using a few drops of sodium hydroxide to raise the pH of my PBS solution - which I will be using in washes during an immunostaining process on sections of ferret brain. Would even a small amount of sodium hydroxide damage the slices? For 1000 mL of PBS, what would you estimate the max amount of sodium hydroxide I should add?

My issue is that the distilled water in our lab is pretty acidic (pH ~5.5-6.0)

[MT Scientist]

Use your pH meter, add NaOH and stop when the you get to the pH you want (I assume Physiological PH).  Just randomly adding NaOH may not get you where you want to be.

As an aside, have you measured the pH of your PBS?  As it is a buffer, it may not need any NaOH, just a bit more of one of the conjugates... 

[jumi08]

I used a digital pH meter and the PBS came to about 7.00 - 7.10; where it should be at 7.40. I had been adding NaOH little by little - I just wasn't sure if it was particularly harmful to slices above a known concentration.

Thanks for the reply.

[jfrasca]

You should be just fine using that to alter the pH of your buffer. I do it all the time, it doesnt hurt the tissue one bit. Just make sure you use a pH meter and do it slowly. I use 0.1N NaOH, add a bit, stir and check pH and repeat until you are at 7.4. Hydrochloric acid will bring you back down if you overshoot it. This will also not hurt the tissue as long as the pH is around 7.4  I use more concentrated base or acid to start off with if my buffer's pH starts way off. This will work with some other buffers like PB, TBS etc.
      Just remember to leave some room for the pH'ing process when you are making your buffer. If you are mixing up your buffer then make sure you dont mess up the concentration by adding tons of diluted NaOH. Leave space for the volume of pH buffering process, the base, and then top off your PBS with ddH20, or whatever you use to its final desired volume That will keep your concentration of PBS from being off.

[MT Scientist]

PBS is a made from monobasic sodium phosphate solution and dibasic sodium phosphate solution mixed together to achieve a particular pH (with the addition of some salt).  Different pHs are achieved by a varying the amount of mono vs. dibasic and not by the addition of NaOH or HCl.