Tris
From Genetics Wiki
tris(hydroxymethyl)aminomethane
Tris acts as a pH buffer to make a solution resistant to changes in pH. It works well as a buffer in the typical physiological pH range.
Safety
MSDS: https://www.sciencelab.com/msds.php?msdsId=9925348
Links
https://en.wikipedia.org/wiki/Tris