ISSN:
1572-8927
Keywords:
HEPPSO
;
emf
;
pK 2
;
zwitterionic buffer
;
ionic strength
;
thermodynamics
;
activity coefficients
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The second acidic dissociation constants pK 2 of the ampholyte N-(2-hydroxyethyl) piperazine-N′-2-hydroxypropanesulfonic acid (HEPPSO) have been determined at seven temperatures from 5 to 55°C from emf measurements utilizing hydrogen and silver–silver chloride cells without liquid junction. The thermodynamic quantities, ΔG°, ΔH°,ΔS°, and Δ C p o have been calculated from the temperature coefficient of pK 2. At 25°C, the pK 2 = 8.042 and at 37°C, pK 2 = 7.876; hence, buffer solutions of HEPPSO and NaHEPPSOate are important for pH control in the region close to that of clinical fluids (blood serum). Conventional pH values from 5 to 55°C as well as those obtained from liquid junction correction at 25 and 37°C have been reported for three buffer solutions with the compositions (molality scale): (1) equimolal mixture of HEPPSO (0.04 m) + NaHEPPSOate (0.04 m) + NaCl (0.12 m); (2) HEPPSO (0.08 m) + NaHEPPSOate (0.08 m); and (3) HEPPSO (0.08 m) + NaHEPPSOate (0.08 m) + NaCl (0.08 m).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1022600604950