Chromatography Forum

Good evening

I’ve read a few posts on here about the ‘right’ and ‘wrong’ way to make up buffers. They are interesting, and apparently it is quite a controversial topic

I have a more academic question, regarding the maths of what’s going on.

For ease, convenience, and reproducibility we favour mixing calculated volumes rather than titration. I’ve also been advised that it’s far more reproducible to mix the buffer components rather than the salts (due to getting wet).

Is there a resource that explains the maths to work out given composition.

E.g. 10mM ammonium acetate can easily be prepared from 10mM ‘ammonia’ and 10mM acetic acid. But if I wanted acid/basic buffered how do I work out how much extra to add to a given pH.

In biology there are a tonne of tables that show exactly how much of x and y to mix to get a given pH but the waters and Agilent buffer prep guides just give the quantities of salt for an x mM solution.

https://en.wikipedia.org/wiki/Henderson ... h_equation

Well-meaning recipe-books telling you to use 1.23g sodium phosphate are intended to deal with the problem that biologists (in particular) are often barely numerate and can't prepare a 10mM solution. But such recipe books cause as much trouble as they solve, because they assume a particular salt, and if someone's bought something with a different amount of water of crystallization, for example, then they will make a solution of a different strength.
Also be aware that you can't use the Henderson-Hasselbalch equation unless you know all the relevant pKa values, and these depend on temperature and solvent-mix.
Preparing solutions by calculated weight and volume can be extremely reproducible (good!), but you won't necessarily get the pH you expected.