The measurement of pH in saline and hypersaline media at sub-zero temperatures: Characterization of Tris buffers.

Papadimitriou, Stathys, Loucaides, Socratis, Rérolle, Victoire, Achterberg, Eric P. , Dickson, Andrew G., Mowlem, Matthew and Kennedy, Hilary (2016) The measurement of pH in saline and hypersaline media at sub-zero temperatures: Characterization of Tris buffers. Open Access Marine Chemistry, 184 . pp. 11-20. DOI 10.1016/j.marchem.2016.06.002.

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Abstract

Highlights

• pH of Tris buffers determined in synthetic seawater and brines with the Harned cell.
• pH determination of Tris buffers to the freezing point of synthetic solutions.
• pH determination of the equimolal and non-equimolal Tris buffer variants.
• pH measurement is facilitated at below-zero temperatures, such as in sea ice brines.

The pH on the total proton scale of the Tris-HCl buffer system (pH(Tris)) was characterized rigorously with the electrochemical Flamed cell in salinity (S) 35 synthetic seawater and S = 45-100 synthetic seawater-derived brines at 25 and 0 degrees C, as well as at the freezing point of the synthetic solutions (-1.93 degrees C at S = 35 to -6 degrees C at S = 100). The electrochemical characterization of the common equimolal Tris buffer [R-Tris = m(Tris)/m(Tris-H+) = 1.0, with m(Tris) = m(Tris-H+) = 0.04 mol kg(H2O)(-1) = molality of the conjugate acid-base pair of 2-amino-2-hydroxymethyl-1,3-propanediol (Tris)] yielded pH(Tris) values which increased with increasing salinity and decreasing temperature. The electrochemical characterization of a non-equimolal Tris buffer variant (R-Tris = 0.5, with m(Tris) = 0.02 mol kg(H2O)(-1) and MTris-H+ = 0.04 mol kg(H2O)(-1)) yielded pH(Tris) values that were consistently less alkaline by 03 pH unit than those of the equimolal Tris buffer. This is in agreement with the values derived from the stoichiometric equilibrium of the Tris-H+ dissociation reaction, described by the Henderson - Hasselbalch equation, pH(Tris) = pK(Tris)* + logR(Tris), with pK(Tris)* = stoichiometric equilibrium dissociation constant of Tris-H+, equivalent to equimolal pH(Tris). This consistency allows reliable use of other R-Tris variants of the Tris-HCl buffer system within the experimental conditions reported here. The results of this study will facilitate the pH measurement in saline and hypersaline systems at below-zero temperatures, such as sea ice brines.

Document Type: Article
Additional Information: WOS:000380080100002
Keywords: Calibration; Standards; pH; Traceability; Sea ice; Brine; Low temperature
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.marchem.2016.06.002
ISSN: 0304-4203
Related URLs:
Projects: Future Ocean
Date Deposited: 06 Sep 2016 09:08
Last Modified: 01 Feb 2019 15:17
URI: http://oceanrep.geomar.de/id/eprint/33727

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