BUFFERS FOR THE PHYSIOLOGICAL PH RANGE - THERMODYNAMICS OF THE 2ND DISSOCIATION OF YDROXYETHYL)PIPERAZINE-N'-2-HYDROXYPROPANESULFONIC ACID FROM 5 TO 55-DEGREES-C

The second acidic dissociation constants pK(2) of the ampholyte N-(2-h ydroxyethyl) piperazine-N'-2-hydroxypropanesulfonic acid (HEPPSO) have been determined at seven temperatures from 5 to 55 degrees C from emf measurements utilizing hydrogen and silver-silver chloride cells with out liquid junction. The thermodynamic quantities, Delta G degrees, De lta H degrees, Delta S degrees, and Delta C(p)degrees have been calcul ated from the temperature coefficient of pK(2). At 25 degrees C, the p K(2) = 8.042 and at 37 degrees C, pK(2) = 7.876; hence, buffer solutio ns of HEPPSO and NaHEPPSOate are important for pH control in the regio n close to that of clinical fluids (blood serum). Conventional pH valu es from 5 to 55 degrees C as well as those obtained from liquid juncti on correction at 25 and 37 degrees C have been reported for three buff er solutions with the compositions (molality scale): (1) equimolal mix ture of HEPPSO (0.04 m) + NaHEPPSOate (0.04 m) + NaCl (0.12 m); (2) HE PPSO (0.08 m) + NaHEPPSOate (0.08 m); and (3) HEPPSO (0.08 m) + NaHEPP SOate (0.08 m) + NaCl (0.08 m).