Buffer Standards for pH Measurement of N-(2-Hydroxyethyl)piperazine-N'-2-ethanesulfonic Acid (HEPES) for I=0.16 mol.kg from 5 to 55 deg C

• Published in: Journal of solution chemistry 2009-04, Vol.38 (4), p.449-458
• Main Authors: Roy, Rabindra N, Roy, Lakshmi N, Ashkenazi, Shahaf, Wollen, Joshua T, Dunseth, Craig D, Fuge, Michael S, Durden, Jared L, Roy, Chandra N, Hughes, Hannah M, Morris, Brett T, Cline, Kevin L
• Format: Article
• Language: English
• ISSN: 0095-9782; 1572-8927
• DOI: 10.1007/s10953-009-9378-3

The values of the second dissociation constant, pK 2, of N-(2-hydroxyethyl) piperazine-N'-2-ethanesulfonic acid (HEPES) have been reported at twelve temperatures over the temperature range 5 to 55 deg C, including 37 deg C. This paper reports the results for the pa H of eight isotonic saline buffer solutions with an I=0.16 mol.kg including compositions: (a) HEPES (0.01 mol.kg) + NaHEPES (0.01 mol.kg) + NaCl (0.15 mol.kg); (b) HEPES (0.02 mol.kg) + NaHEPES (0.02 mol.kg) + NaCl (0.14 mol.kg); (c) HEPES (0.03 mol.kg) + NaHEPES (0.03 mol.kg) + NaCl (0.13 mol.kg); (d) HEPES (0.04 mol.kg) + NaHEPES (0.04 mol.kg) + NaCl (0.12 mol.kg); (e) HEPES (0.05 mol.kg) + NaHEPES (0.05 mol.kg) + NaCl (0.11 mol.kg); (f) HEPES (0.06 mol.kg) + NaHEPES (0.06 mol.kg) + NaCl (0.10 mol.kg); (g) HEPES (0.07 mol.kg) + NaHEPES (0.07 mol.kg) + NaCl (0.09 mol.kg); and (h) HEPES (0.08 mol.kg) + NaHEPES (0.08 mol.kg) + NaCl (0.08 mol.kg). Conventional pa H values, for all eight buffer solutions from 5 to 55 deg C, have been calculated. The operational pH values with liquid junction corrections, at 25 and 37 deg C have been determined based on the NBS/NIST standard between the physiological phosphate standard and four buffer solutions. These are recommended as pH standards for physiological fluids in the range of pH = 7.3 to 7.5 at I=0.16 mol.kg.