What is the difference between the usages of bis-tris methane and bis-tris propane? I came across "bis-tris" buffer in Rodney Boyer's _Biochemistry Laboratory_ book and tried looking it up. Then I found that there's bis-tris methane and bis-tris propane that are both buffers. What exactly are they used for and are the usages different?

They have different acid dissociation equilibria and so buffer at different pH.


pKa1 pKa2
Bis-Tris methane 6.5 -
Bis-Tris propane 6.8 9


[source]

The two titratable secondary amines of Bis-Tris propane make it usable over a wider pH range.