pHT measurements of TRIS buffer solutions in an artificial seawater matrix in the salinity range 5–40 and temperature range 5–40 °C. Part 1: Measurements and data fitting

Capitaine, Gaëlle, Schäfer, Rieke, Bastkowski, Frank, Stoica, Daniela, Pellegrino, Olivier, Quendera, Raquel, Achterberg, Eric P., Wagener, Thibaut, Clegg, Simon L., Seitz, Steffen and Fisicaro, Paola (2025) pHT measurements of TRIS buffer solutions in an artificial seawater matrix in the salinity range 5–40 and temperature range 5–40 °C. Part 1: Measurements and data fitting. Marine Chemistry, 273. ISSN 0304-4203

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Abstract

Spectrophotometric measurements of seawater total pH (pHT) contribute to the knowledge of the oceanic carbonate system, and hence to the assessment of the ocean carbon cycle and the monitoring of ocean acidification. Spectrophotometric measurements rely on the characterization of the indicator dye's second dissociation constant, obtained from measurements on solutions of known pHT. Therefore, Harned cell potentiometric measurements were performed on equimolal TRIS buffers (i.e. buffers containing equal molalities of 2-amino-2-(hydroxymethyl)-1,3-propanediol (TRIS, CAS reference number 77–86-1) and TRIS hydrochloride (TRIS.HCl)), made in an artificial seawater (ASW) matrix. Buffer solutions were prepared in an ASW matrix of nominal practical salinities from 5 to 40, and Harned cell measurements were performed on these solutions at temperatures from 5 °C to 40 °C. This provides, for the first time, pHT values of ASW/TRIS buffers that are consistent for the entire ranges of salinity relevant for oceanographic measurements, and for a wide range of temperature. The work presented includes a comparison of results from three National Metrology Institutes to assess reproducibility, and provides a function allowing the calculation of equimolal ASW/TRIS buffers pHT as a function of salinity, temperature and TRIS buffer molality. This function can be used to derive pHT values for zero TRIS molality, thus representing a pure ASW (i.e. a chemical environment unaffected by the presence of TRIS and TRIS.HCl), and referring to a true pHT scale. These values are needed for the characterization of the second dissociation constant of the dye with perspective of traceability to the International System of units.

Item Type:	Article
Uncontrolled Keywords:	ocean acidification,total ph,traceability,tris buffer,oceanography,environmental chemistry,chemistry(all),water science and technology ,/dk/atira/pure/subjectarea/asjc/1900/1910
Faculty \ School:	Faculty of Science > School of Environmental Sciences
UEA Research Groups:	Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
Related URLs:	http://www.scopus.com/inward/record.url?...
Depositing User:	LivePure Connector
Date Deposited:	27 Mar 2026 11:30
Last Modified:	27 Mar 2026 11:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/102611
DOI:	10.1016/j.marchem.2025.104551

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