{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,11]],"date-time":"2026-02-11T15:01:15Z","timestamp":1770822075468,"version":"3.50.1"},"reference-count":19,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2021,9,15]],"date-time":"2021-09-15T00:00:00Z","timestamp":1631664000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100014132","name":"European Metrology Programme for Innovation and Research","doi-asserted-by":"publisher","award":["17FUN09 UnipHied"],"award-info":[{"award-number":["17FUN09 UnipHied"]}],"id":[{"id":"10.13039\/100014132","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Water"],"abstract":"<jats:p>Fluctuations of pH in coastal systems are generally surveyed through potentiometric pH measurements. A new concept of a unified pH scale was introduced with the great advantage of enabling comparability of absolute values, pHabs, pertaining to any medium. Using water as an anchor solvent, yielding pHabsH2O, enables referencing the pHabs values to the conventional aqueous pH scale. The current work aims at contributing to implement pHabsH2O to saline solutions. To this purpose, differential potentiometric measurements, with a salt bridge of ionic liquid [N2225][NTf2], were carried out aiming at overcoming problems related to residual liquid junction potentials that affect the quality of such measurements. The ability to measure pHabsH2O with acceptable uncertainty was evaluated using Tris-Tris\u00b7HCl standard buffer solutions prepared in a background matrix close to the characteristics of estuarine systems (salinity of 20) as well as with NaCl solutions with ionic strength between 0.005 and 0.8 mol kg\u22121. The present study shows that for high ionic strength solutions, such as seawater, challenges remain when addressing the assessment and quantification of ocean acidification in relation to climate change. Improvements are envisaged from the eventual selection of a more adequate ionic liquid.<\/jats:p>","DOI":"10.3390\/w13182522","type":"journal-article","created":{"date-parts":[[2021,9,14]],"date-time":"2021-09-14T23:34:11Z","timestamp":1631662451000},"page":"2522","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Toward Unified pH of Saline Solutions"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7928-6125","authenticated-orcid":false,"given":"Silvie","family":"Lainela","sequence":"first","affiliation":[{"name":"Department of Marine Systems, Tallinn University of Technology, Akadeemia tee 15a, 12618 Tallinn, Estonia"},{"name":"Institute of Chemistry, University of Tartu (UT), 14a Ravila Street, 50411 Tartu, Estonia"},{"name":"Laboratoire National de M\u00e9trologie et d\u2019Essais (LNE), 1 Rue Gaston Boissier, 75015 Paris, France"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3000-4964","authenticated-orcid":false,"given":"Ivo","family":"Leito","sequence":"additional","affiliation":[{"name":"Institute of Chemistry, University of Tartu (UT), 14a Ravila Street, 50411 Tartu, Estonia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0893-8015","authenticated-orcid":false,"given":"Agnes","family":"Heering","sequence":"additional","affiliation":[{"name":"Institute of Chemistry, University of Tartu (UT), 14a Ravila Street, 50411 Tartu, Estonia"}]},{"given":"Ga\u00eblle","family":"Capitaine","sequence":"additional","affiliation":[{"name":"Laboratoire National de M\u00e9trologie et d\u2019Essais (LNE), 1 Rue Gaston Boissier, 75015 Paris, France"}]},{"given":"B\u00e1rbara","family":"Anes","sequence":"additional","affiliation":[{"name":"FCi\u00eancias. ID (FC.ID), Centro de Qu\u00edmica Estrutural, Faculdade de Ci\u00eancias da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8582-8904","authenticated-orcid":false,"given":"Filomena","family":"Cam\u00f5es","sequence":"additional","affiliation":[{"name":"FCi\u00eancias. ID (FC.ID), Centro de Qu\u00edmica Estrutural, Faculdade de Ci\u00eancias da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal"}]},{"given":"Daniela","family":"Stoica","sequence":"additional","affiliation":[{"name":"Laboratoire National de M\u00e9trologie et d\u2019Essais (LNE), 1 Rue Gaston Boissier, 75015 Paris, France"}]}],"member":"1968","published-online":{"date-parts":[[2021,9,15]]},"reference":[{"key":"ref_1","unstructured":"Newton, J.A., Feely, R.A., Jewett, E.B., Williamson, P., and Mathis, J. (2021, July 22). Global Ocean Acidification Observing Network: Requirements and Governance Plan, Available online: http:\/\/www.goa-on.org\/documents\/general\/GOA-ON_2nd_edition_final.pdf."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"S58","DOI":"10.1002\/lno.10738","article-title":"Inferring scale-dependent processes influencing stream water biogeochemistry from headwater to sea","volume":"62","author":"Tiwari","year":"2017","journal-title":"Limnol. Oceanogr."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"2169","DOI":"10.1351\/pac200274112169","article-title":"Measurement of pH. Definition, standards, and procedures","volume":"74","author":"Buck","year":"2002","journal-title":"Pure Appl. Chem."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"R26","DOI":"10.1088\/0026-1394\/53\/1\/R26","article-title":"Metrological challenges for measurements of key climatological observables. Part 3: Seawater pH","volume":"53","author":"Dickson","year":"2015","journal-title":"Metrologia"},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Stoica, D., Anes, B., Fisicaro, P., and Cam\u00f5es, M.F. (2021). Feasibility of multifunction calibration of H+ responsive glass electrodes in seawater. J. Pure Appl. Chem.","DOI":"10.1515\/pac-2020-0202"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"118","DOI":"10.1016\/j.talanta.2018.09.075","article-title":"Seawater pH measurements with a combination glass electrode and high ionic strength TRIS-TRIS HCl reference buffers\u2014An uncertainty evaluation approach","volume":"193","author":"Anes","year":"2019","journal-title":"Talanta"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"778","DOI":"10.1007\/s00216-002-1506-5","article-title":"Traceability of pH measurements by glass electrode cells: Performance characteristic of pH electrodes by multi-point calibration","volume":"374","author":"Naumann","year":"2002","journal-title":"Anal. Bioanal. Chem."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1661","DOI":"10.1007\/s10008-011-1373-0","article-title":"Salt bridge in electroanalytical chemistry: Past, present, and future","volume":"15","author":"Kakiuchi","year":"2011","journal-title":"J. Solid State Electrochem."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"2344","DOI":"10.1002\/anie.201707333","article-title":"The Ideal ionic liquid salt bridge for the direct determination of gibbs energies of transfer of single ions, Part I: The concept","volume":"57","author":"Radtke","year":"2018","journal-title":"Angew. Chem."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"2348","DOI":"10.1002\/anie.201707334","article-title":"The ideal ionic liquid salt bridge for direct determination of gibbs energies of transfer of single ions, Part II: Evaluation of the role of ion solvation and ion mobilities","volume":"57","author":"Ermantraut","year":"2018","journal-title":"Angew. Chem."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"2623","DOI":"10.1021\/ac504692m","article-title":"Unified pH values of liquid chromatography mobile phases","volume":"87","author":"Suu","year":"2015","journal-title":"Anal. Chem."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"4020","DOI":"10.1021\/acs.est.8b03655","article-title":"Drivers of pH variability in coastal ecosystems","volume":"53","author":"Carstensen","year":"2019","journal-title":"Environ. Sci. Technol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"113","DOI":"10.1016\/0021-9614(90)90074-Z","article-title":"Standard potential of the reaction: AgCl (s)+ 12H2 (g)= Ag (s)+ HCl (aq), and the standard acidity constant of the ion HSO4- in synthetic sea water from 273.15 to 318.15 K","volume":"22","author":"Dickson","year":"1990","journal-title":"J. Chem. Thermodyn."},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Heering, A., Stoica, D., Cam\u00f5es, F., Anes, B., Nagy, D., Nagyn\u00e9 Szil\u00e1gyi, Z., Quendera, R., Ribeiro, L., Bastkowski, F., and Born, R. (2020). Symmetric potentiometric cells for the measurement of unified pH values. Symmetry, 12.","DOI":"10.3390\/sym12071150"},{"key":"ref_15","unstructured":"Bastkowski, F., and Heering, A. EMPIR JRP FUN-09 realisation of a unified pH scale\u2014Deliverable 2\u2014Report on interlaboratory comparison to evaluate the performance of measurement procedures, (unpublished work)."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1007\/s00769-015-1163-y","article-title":"Compatibility of activity coefficients estimated experimentally and by Pitzer equations for the assessment of seawater pH","volume":"21","author":"Anes","year":"2016","journal-title":"Accredit. Qual. Assur."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"4247","DOI":"10.3390\/w7084247","article-title":"Traceability of pH to the Mole","volume":"7","author":"Anes","year":"2015","journal-title":"Water"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Radtke, V., Stoica, D., Leito, I., Cam\u00f5es, F., Krossing, I., Anes, B., Rozikov\u00e1, M., Deleebeeck, L., Veltz\u00e9, S., and N\u00e4ykki, T. (2021). A unified pH scale for all solvents Part I Intention and Reasoning. J. Pure Appl. Chem.","DOI":"10.1515\/pac-2019-0504"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"549","DOI":"10.1021\/acssensors.8b01651","article-title":"Reference electrodes with ionic liquid salt bridge: When will these innovative novel reference electrodes gain broad acceptance?","volume":"4","author":"Lindner","year":"2019","journal-title":"ACS Sens."}],"container-title":["Water"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-4441\/13\/18\/2522\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T07:02:55Z","timestamp":1760166175000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-4441\/13\/18\/2522"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,9,15]]},"references-count":19,"journal-issue":{"issue":"18","published-online":{"date-parts":[[2021,9]]}},"alternative-id":["w13182522"],"URL":"https:\/\/doi.org\/10.3390\/w13182522","relation":{},"ISSN":["2073-4441"],"issn-type":[{"value":"2073-4441","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,9,15]]}}}