Feasibility of multifunction calibration of H+-responsive glass electrodes in seawater (IUPAC Technical Report)

doi:10.1515/ci-2022-0123

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Feasibility of multifunction calibration of H⁺-responsive glass electrodes in seawater (IUPAC Technical Report)

Published/Copyright: January 25, 2022

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From the journal Chemistry International Volume 44 Issue 1

Daniela Stoica, Bárbara Velasco Anes, Paola Fisicaro, and Maria Filomena Camões

Pure and Applied Chemistry, 2021

Vol. 93, no. 12, pp. 1487-1497

https://doi.org/10.1515/pac-2020-0202

Seawater pH values are of the highest relevance in marine chemistry studies, not only through being acidity indicators but also due to the control provided by H⁺(aq) over the various simultaneous equilibria occurring in seawater. Although the concept of pH = −lga_H⁺ = −lg(m_H⁺γ_H⁺/m⁰), where m_H⁺ is the relative (molality basis) activity, γ_H⁺ is the molal activity coefficient of the hydrogen ion H⁺ at molality m_H⁺, and m⁰ is the standard molality, was introduced in 1910 and reaffirmed on successive occasions by relevant bodies, different conceptual definitions and alternative measurement procedures have been adopted and are in use by some, namely among oceanographers, often leading to confusion. This leads to major difficulties with the use of data, e.g., on what concerns comparison of results in space and time. Primary pH values, the highest quality level in terms of the metrological chain, have been assigned to primary reference pH buffer solutions of low ionic strength, by a primary method based on measurements of the Harned cell potential in association with the Nernst equation, as well as on the adoption of extra-thermodynamic model assumptions for electrolyte solutions. Although equivalent types of recommendations dealing with standards and procedures based on metrological traceability are still lacking for higher ionic strength media, as it is in the case of seawater, reference Tris–Tris·HCl buffer solutions in artificial seawater have been suggested for use in the calibration of pH meter systems. In this work, Tris–Tris·HCl buffer saline solutions of three different molality ratios have been assigned reference values and multi-point calibration of pH meters in terms of either pH or pH^T is thus possible and supports measurement of their respective values under routine conditions at a high metrological level.

Online erschienen: 2022-01-25

Erschienen im Druck: 2022-01-01

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https://doi.org/10.1515/ci-2022-0123