Measurement of pH of Blood and Other Physiological Media To the Editor:

Buffer solutions for pH control in the range of dissociation constants of weak acids (10 to 106) are numerous, But the suitability of a buffer system in the physiologically important pH range (pH values of 6 to 8) is rendered difficult by the scarcity of weak acid-base systems with pK’s between 6 and 8. Another hindering factor is the incompatibility of some acid-salt buffers with physio-logical media (1, 2). For example, the primary pH standard phosphate buf-fers, certified by the National Bureau of Standards, precipitate calcium and react with certain other blood constituents. An attempt to avoid this kind of diffi-culty has been made by Durst and Sta-ples (3), Bates and Allen (4), and others through the use of nitrogenous bases and their salts. For example, in the pH range of 7 to 9, the most widely used buffer is tri(hydroxymethyl)methyl-amine (Tris) and its hydrochloride (3); despite certain other advantages, Tris lacks good buffering capacity below a pH of 7.5 and is quite reactive because of the presence of a primary aliphatic amine group. In response to the limitations out-lined above, Good et al. (5) selected 12 new buffer substances for biological pH control. Attention has recently been focused on Tricine (6), N-[tris