Realisation of a Unified pH Scale

doi:10.1515/ci-2018-0416

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Realisation of a Unified pH Scale

Published/Copyright: October 29, 2018

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From the journal Chemistry International Volume 40 Issue 4

Hydrogen ions, H⁺, play an important role in virtually all material-related processes and the pH of solutions is probably the most prominent chemical concept widely used, thus building interdisciplinary bridges. Accurate measurement of pH values is an extremely important task in a wide variety of media in which the processes occur, i.e., water or solvents other than water, solvent mixtures, and dispersions. The concept of pH is very well defined and routinely used in dilute aqueous solutions. Values of pH in different media are related through the proton Gibbs free energy of exchange between solvents, but even at the theoretical level, valid comparability of pH values in different media has been impossible. Values measured in one medium can only be loosely correlated to those measured in other media, hence hindering the possibility of conversion into each other at the necessary level of accuracy.

In 2010, the unified acidity (pHabs) concept, based on the hydrogen ion chemical potential, was introduced [1] enabling comparability of pH values between all phases. Nevertheless, putting this concept into practical use has proved tremendously difficult, requiring the not-straightforward knowledge of physicochemical quantities and, in addition, suitable measurement and calibration procedures. Considerable progress has been made with the development and implementation of a potentiometric setup using differential cells [02] partially overcoming difficulties associated with H⁺ selective electrode and liquid junction potentials.

Aiming at developing a practical and reliable method of measuring and expressing acidity of any medium on a universal scale (pHabs), based on a solvent-independent standard state, a project UnipHied (project 17FUN09^[*]), with a 1 May 2018 start date and a duration of 36 months, has been approved and funded from the EMPIR programme, from the Participating States and from the European Union’s Horizon 2020 research and innovation programme. The partners of the UnipHied network are LNE (France, coordinator), BFKH (Hungary), CMI (Czech Republic), DFM (Denmark), IPQ (Portugal), PTB (Germany), SYKE (Finland), TUBITAK-UME (Turkey), ALU-FR (Germany), ANBSensors (United Kingdom), FCiencias.ID (Portugal), and UT (Estonia).

The central goal of UnipHied is to put the new, theoretical concept of the recently introduced unified pHabs scale on a metrologically well-founded basis into practice.

The most important specific objectives of UnipHied are: (1) to develop and validate a reliable and universally applicable measurement procedure that enables the measurement of pHabs; (2) to create a reliable method for the experimental or computational evaluation of the liquid junction potential between aqueous and non-aqueous solutions; (3) to develop a coherent and validated suite of calibration standards for standardizing routine measurement systems in terms of pHabs values for a variety of widespread systems (e.g., industrial mixtures, soils/waters, food products, biomaterials).

Impact is envisaged on industrial and other user communities, metrology and scientific applications, and on relevant standards, all of which will lead to wider economic, social, and environmental impacts.

A stakeholder committee will contribute to clarify the needs of the various end-user communities and to give advice on the project progress in terms of how to make the outcomes the most useful to practitioners. The interaction will be achieved with meetings, typically held in conjunction with the project meetings, in order to foster the collaboration between the NMIs and universities, and end-users communities.

IUPAC is one of the project stakeholders and the link with UnipHied will be ensured through the Analytical Chemistry Division, namely its Subcommittee on pH. Information will be regularly exchanged and Technical Reports will be prepared for publication in the IUPAC official journal, seeking the further approval and recommendation of methods and procedures that reflect universal acceptance of the unified pHabs scale by the scientific community, thus supporting their usage.

For more information and comments, contact Maria Filomena Camões <fcamoes@fc.ul.pt>, Chair of the Subcommittee on pH

https://iupac.org/body/504

References:

1. Himmel, D.; Goll, S. K.; Leito, I.; Krossing, I. Angew. Chem. Int. Ed. 2010, 49, 6885–688810.1002/anie.201000252Search in Google Scholar PubMed

2. Suu, A.; Jalukse, L.; Liigand, J.; Kruve, A.; Himmel, D.; Krossing, I.; Rosés, M.; Leito, I. Anal. Chem. 2015, 87, 2623-2630 10.1021/ac504692mSearch in Google Scholar PubMed

Online erschienen: 2018-10-29

Erschienen im Druck: 2018-10-01

©2018 IUPAC & De Gruyter. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. For more information, please visit: http://creativecommons.org/licenses/by-nc-nd/4.0/

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https://doi.org/10.1515/ci-2018-0416