Isaac B. Henson

Buffer Standards for the Physiological pH of N-(2-Hydroxyethyl) piperazine-N'-4-butanesulfonic Acid (HEPBS) from 5 to 55 °C

The pH values of six buffer solutions of equal compositions on the molal scale and eight buffer solutions hav- ing ionic strengths (I = 0.16 mol·kg -1 ) similar to the concentration of blood plasma have been evaluated at 12 temperatures from 5 to 55 °C using the Bates-Guggenheim convention and extended Debye-Huckel equation. The values of Ej for the buffer solution of HEPBS have been obtained from the flowing junction cell measurement. These values of Ej have been used to ascertain the operational pH values at 25 and 37 °C for HEPBS buffer solution. The pH values at 25 and 37 °C are 7.415 and 7.395, respectively, for physiological phosphate buffer solutions. The zwitterionic buffer HEPBS was shown to be useful as a secondary pH standard in the region close to that of blood serum.

Standards for pH Measurements of Bis-((2-Hydroxyethyl)amino)acetic Acid (BICINE) from (278.15 to 328.15) K

The second dissociation constant, pK2, and related thermodynamic data for BICINE have been previously de- termined and reported from temperatures (278.15 to 328.15) K. For the present study, three buffer solutions without NaCl, and five with NaCl yielding an ionic strength (I = 0.16 mol·kg -1 ) similar to that of blood plasma were prepared. These buffer solutions have been evaluated in the temperature range of (278.15 to 328.15) K using the extended form of the De- bye-Huckel equation. The Bates-Guggenheim convention is only valid when I< 0.1 mol·kg -1 . Values of the residual liquid junction potential (δEj) between the BICINE solutions and the saturated KCl calomel electrode have been estimated at (298.15 and 310.15) K. Two BICINE buffer solutions are recommended as primary standard reference solutions for pH measurements of biological fluids.