2ND DISSOCIATION-CONSTANT OF 2-SUBSTITUTED AMINOMETHANESULFONIC ACIDSIN WATER FROM 5 TO 55-DEGREES-C

The equilibrium constants for the dissociation steps of (4-morpholinee thanesulfonic acid) (MES) and (2-{[tris(hydroxymethyl)methyl]-1-ethane sulf acid (TES) have been determined at 12 and 7 different temperature s, respectively, from 5 to 55 degrees C. The emf measurements were car ried out by using a cell without liquid junction of the type: Pt; H-2 (g, 1 atm) \ buffer(ml), Na salt of buffer(m(2)), NaCl(m(3)) \ AgCl, A g. The pK(2) values of MES and TES at 25 degrees C are 6.269 and 7.550 . The thermodynamic quantities for the dissociation process have been calculated. These zwitterionic compounds are useful for pH control as standard buffers in the physiological region of pH 5.50 to 6.50 for ME S, 6.5 to 7.5 for TES, respectively. Reliable measurements of the pH a t isotonic saline solution (I = 0.16m) such as blood and plasma are im portant for clinical diagnosis.