[Babcock_Hall]

I am aware that Tris buffer, a.k.a. THAM or Tris(hydroxymethyl)amino methane), is not compatible with some or all gel-filled electrodes, but what about glycine?  I was planning to prepare two glycine buffers (pH 9 and pH 10).  The pK_a2 for glycine is about 9.8, and it is a primary amine.

[Babcock_Hall]

I had my students make a total of six buffers (all 0.1 M), and I remeasured the pH values today.  Three were close to what the students had measured (less than or equal to 0.1 pH unit).  Given that the students were using relatively old electrodes, I wasn't expecting perfect agreement.  Two of the three that were far away from what the students measured were glycine at high pH ( >9).  The third that was far out (>0.2 pH unit) was phosphate.

If it were not for the phosphate result, I might be inclined to conclude either that high pH buffers were more problematic, or that glycine is problematic.  Any thoughts?