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Pure Appl. Chem., 2007, Vol. 79, No. 1, pp. 81-86

doi:10.1351/pac200779010081

ANALYTICAL CHEMISTRY DIVISION

Guidelines for potentiometric measurements in suspensions Part B. Guidelines for practical pH measurements in soil suspensions (IUPAC Recommendations 2006)

Srecko F. Oman1, M. Filomena Camões2, Kipton J. Powell3, Raj Rajagopalan4, and Petra Spitzer5

1Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, 1000 Ljubljana, Slovenia; 2Departamento de Química e Bioquímica, University of Lisbon (CECUL/DQB), Faculdade de Sciências da Universidade de Lisboa, Edificio C8, Pt-1749-016, Lisboa, Portugal; 3Department of Chemistry, University of Canterbury, Christchurch, New Zealand; 4Department of Chemical and Biomolecular Engineering, National University of Singapore, 117576, The Republic of Singapore; 5Physikalisch-Technische Bundesanstalt (PTB), Postfach 3345, D-38023, Braunschweig, Germany

Abstract: The measured cell potentials for suspension potentiometric cells have been interpreted and explained by a detailed analysis of the schemes for these cells ["Guidelines for potentiometric measurements in suspensions. Part A. The suspension effect (IUPAC Technical Report", Pure Appl. Chem. 79, 67 (2007)]. Some former disagreements amongst investigations have been clarified. A new unambiguous operational definition of the suspension effect (SE) is presented. It is defined as the difference in cell potential for two suspension potentiometric cells, one with both electrodes in the separated equilibrium solution (eqs) and the other with both electrodes in the sediment or suspension. This potential difference is the sum of the change in the indicator electrode (IE) potential and the change in the liquid junction potential of the reference electrode (RE), when the electrodes are used for measurement, once in the sediment of the suspension and then in its eqs.

Keywords: anomalous liquid junction potential; boundary potential; IUPAC Analytical Chemistry Division; mixed potential; operational definition of suspension effect; pH; pIon; soil pH; suspension effect; suspension potentiometric cell.

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