Buffers for the physiological pH range: thermodynamic constants of four substituted aminoethanesulfonic acids from 5 to 50 degrees C

Vega, C.A.; Bates, R.G.

Analytical Chemistry 48(9): 1293-1296


ISSN/ISBN: 0003-2700
PMID: 182042
DOI: 10.1021/ac50003a010
Accession: 068523220

Download citation:  

Article/Abstract emailed within 0-6 h
Payments are secure & encrypted
Powered by Stripe
Powered by PayPal

The pK2 values for 4 N-substituted aminoethanesulfonic acids were determined at 10 temperatures in the range 5-50.degree. C. The dissociation constants were derived from the emf of cells without liquid junction, utilizing H electrodes and Ag-AgBr electrodes, and the thermodynamic quantities .DELTA.H.degree. were calculated from the temperature coefficients of the dissociation constants. The pK2 values at 25.degree. C are 6.270 (MES), 7.187 (BES), 7.550 (TES) and 7.565 (HEPES). N-Substitution lowers the pK2 of taurine and, with the exception of HEPES, pK2, .DELTA.H.degree., .DELTA.S.degree. and .DELTA.Cp.degree. form a regular series for the remaining 4 compounds. TES and HEPES are especially useful for pH control and possibly as standards in the pH region close to that of blood serum.