Multifunction Calibration of H+ Responsive Glass Electrodes in Seawater
Multifunction Calibration of H+ Responsive Glass Electrodes in Seawater
Abstract:
Seawater pH values are of the highest relevance in marine chemistry studies, not only through being acidity indicators but also due to the control played by H+(aq) over the various simultaneous equilibria occurring in seawater. Although the concept of pH = − lgaH+ has been introduced in 1910 and reaffirmed in 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 Harned cell potential in association with Nernst equation as of well as on the adoption extra-thermodynamic model assumptions for electrolyte solutions. While equivalent type of recommendations is still lacking for higher ionic strength media, as it is the case of seawater, reference Tris-TrisHCl buffer solutions in artificial seawater (ASW), have become of widespread use for the calibration of pH meter setups.
In this work Tris-TrisHCl buffer saline solutions of three different molality ratio compositions have been assigned pH = −lgaH+, p𝑚H = −lg𝑚H+ and pHT = − lg(𝑚′′H+ + 𝑚HSO4 −) reference values, aiming at calibration of pH meters in terms of either quantity, hence measurement of their respective values under routine conditions.
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 Harned cell potential in association with Nernst equation as of well as on the adoption extra-thermodynamic model assumptions for electrolyte solutions. While equivalent type of recommendations is still lacking for higher ionic strength media, as it is the case of seawater, reference Tris-TrisHCl buffer solutions in artificial seawater (ASW), have become of widespread use for the calibration of pH meter setups.
In this work Tris-TrisHCl buffer saline solutions of three different molality ratio compositions have been assigned pH = −lgaH+, p𝑚H = −lg𝑚H+ and pHT = − lg(𝑚′′H+ + 𝑚HSO4 −) reference values, aiming at calibration of pH meters in terms of either quantity, hence measurement of their respective values under routine conditions.