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

The measurement of pH in saline and hypersaline media at sub-zero temperatures: characterization of Tris buffers
The measurement of pH in saline and hypersaline media at sub-zero temperatures: characterization of Tris buffers
The pH on the total proton scale of the Tris-HCl buffer system (pHTris) was characterized rigorously with the electrochemical Harned cell in salinity (S) 35 synthetic seawater and S = 45–100 synthetic seawater-derived brines at 25 and 0 °C, as well as at the freezing point of the synthetic solutions (?1.93 °C at S = 35 to ?6 °C at S = 100). The electrochemical characterization of the common equimolal Tris buffer [RTris = mTris/mTris?H+ = 1.0, with mTris = mTris?H+ = 0.04 mol kgH2O?1 = molality of the conjugate acid-base pair of 2-amino-2-hydroxymethyl-1,3-propanediol (Tris)] yielded pHTris values which increased with increasing salinity and decreasing temperature. The electrochemical characterization of a non-equimolal Tris buffer variant (RTris = 0.5, with mTris = 0.02 mol kgH2O?1 and mTris?H+ = 0.04 mol kgH2O?1) yielded pHTris values that were consistently less alkaline by 0.3 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, pHTris = pKTris? + logRTris, with pKTris? = stoichiometric equilibrium dissociation constant of Tris-H+, equivalent to equimolal pHTris. This consistency allows reliable use of other RTris 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.
Calibration, Standards, pH, Traceability, Sea ice, Brine, Low temperature
0304-4203
11-20
Papadimitriou, Stathys
127a801b-c64a-4287-811b-e1c56407edd5
Loucaides, Socratis
5d0c31a4-269d-44a5-a858-13dc609ae072
Rerolle, Victoire
4d877740-df8d-46f4-acfa-62c381491948
Achterberg, Eric P.
685ce961-8c45-4503-9f03-50f6561202b9
Dickson, Andrew G.
225290d7-686a-4ce2-a960-18fa1447a611
Mowlem, Matthew
6f633ca2-298f-48ee-a025-ce52dd62124f
Kennedy, Hilary
932c7e9a-772b-4610-8d57-bdfcee9fd791
Papadimitriou, Stathys
127a801b-c64a-4287-811b-e1c56407edd5
Loucaides, Socratis
5d0c31a4-269d-44a5-a858-13dc609ae072
Rerolle, Victoire
4d877740-df8d-46f4-acfa-62c381491948
Achterberg, Eric P.
685ce961-8c45-4503-9f03-50f6561202b9
Dickson, Andrew G.
225290d7-686a-4ce2-a960-18fa1447a611
Mowlem, Matthew
6f633ca2-298f-48ee-a025-ce52dd62124f
Kennedy, Hilary
932c7e9a-772b-4610-8d57-bdfcee9fd791

Papadimitriou, Stathys, Loucaides, Socratis, Rerolle, 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. Marine Chemistry, 184, 11-20. (doi:10.1016/j.marchem.2016.06.002).

Record type: Article

Abstract

The pH on the total proton scale of the Tris-HCl buffer system (pHTris) was characterized rigorously with the electrochemical Harned cell in salinity (S) 35 synthetic seawater and S = 45–100 synthetic seawater-derived brines at 25 and 0 °C, as well as at the freezing point of the synthetic solutions (?1.93 °C at S = 35 to ?6 °C at S = 100). The electrochemical characterization of the common equimolal Tris buffer [RTris = mTris/mTris?H+ = 1.0, with mTris = mTris?H+ = 0.04 mol kgH2O?1 = molality of the conjugate acid-base pair of 2-amino-2-hydroxymethyl-1,3-propanediol (Tris)] yielded pHTris values which increased with increasing salinity and decreasing temperature. The electrochemical characterization of a non-equimolal Tris buffer variant (RTris = 0.5, with mTris = 0.02 mol kgH2O?1 and mTris?H+ = 0.04 mol kgH2O?1) yielded pHTris values that were consistently less alkaline by 0.3 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, pHTris = pKTris? + logRTris, with pKTris? = stoichiometric equilibrium dissociation constant of Tris-H+, equivalent to equimolal pHTris. This consistency allows reliable use of other RTris 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.

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Accepted/In Press date: 8 June 2016
Published date: 20 August 2016
Keywords: Calibration, Standards, pH, Traceability, Sea ice, Brine, Low temperature
Organisations: Ocean and Earth Science, Ocean Technology and Engineering

Identifiers

Local EPrints ID: 398555
URI: http://eprints.soton.ac.uk/id/eprint/398555
ISSN: 0304-4203
PURE UUID: e3c9d194-1967-45be-941e-b1b737842860

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Date deposited: 26 Jul 2016 10:10
Last modified: 08 Jan 2022 15:36

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Contributors

Author: Stathys Papadimitriou
Author: Socratis Loucaides
Author: Victoire Rerolle
Author: Andrew G. Dickson
Author: Matthew Mowlem
Author: Hilary Kennedy

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