Chemistry International Blank Image
Chemistry International Text Image Link to Chemistry International Blank Image Chemistry International Blank Image Chemistry International Blank Image
Chemistry International Blank Image
Chemistry International Blank Image
Chemistry International Text Image Link to Current Issue
Chemistry International Text Image Link to Past Issues
Chemistry International Text Image Link to Officer's Columns
Chemistry International Text Image Link to Features
Chemistry International Blank Image
Chemistry International Text Image Link to Up for Discussion
Chemistry International Text Image Link to IUPAC Wire
Chemistry International Text Image Link to Project Place
Chemistry International Text Image Link to imPACt
Chemistry International Text Image Link to Bookworm
Chemistry International Text Image Link to Internet Connections
Chemistry International Text Image Link to Conference Call
Chemistry International Text Image Link to Where 2B and Y
Chemistry International Text Image Link to Symposia
Chemistry International Text Image Link to CI Indexes
Chemistry International Text Image Link to CI Editor
Chemistry International Text Image Link to Search Function
Chemistry International Text Image Link to Information

 

Chemistry International Text Image Link to Previous Issue Chemistry International Text Image Link to Previous Page Chemistry International Text Image Link to This TOC Chemistry International Text Image Link to Next Page Chemistry International Text Image Link to Next Issue

Vol. 29 No. 4
July-August 2007

Making an imPACt | Recent IUPAC technical reports and recommendations that affect the many fields of pure and applied chemistry.
See also www.iupac.org/publications/pac

Guidelines for Potentiometric Measurements in Suspensions

Srecko F. Oman, M. Filomena Camões, Kipton J. Powell, Raj Rajagopalan, and Petra Spitzer

Part A. The Suspension Effect (IUPAC Technical Report)
Pure and Applied Chemistry
Vol. 79, No. 1, pp. 67–79, 2007
doi:10.1351/pac200779010067

Part B. Guidelines for Practical pH Measurements in Soil Suspensions (IUPAC Recommendations 2006)
Pure and Applied Chemistry
Vol. 79, No. 1, pp. 81–86, 2007
doi:10.1351/pac200779010081

An explanation of the origin and interpretation of the suspension effect (SE) is presented in accordance with “pH Measurement: IUPAC Recommendations 2002” [Pure Appl. Chem. 74, 2169 (2002)]. It is based on an analysis of detailed schemes of suspension potentiometric cells and confirmed with experimental results. Historically, the term “suspension effect” evolved during attempts to determine electrochemically the thermodynamically defined activity of H+ (aq) in suspensions. The experimental SE arises also in determining other pIon values, analogous to pH values.

The SE relates to the observation that for the potential generated when a pair of electrodes (e.g., reference electrode (RE) and glass electrode) is placed in a suspension, the measured cell voltage is different from that measured when they are both placed in the separate equilibrium solution (eqs). The SE is defined here as the sum of (1) the difference between the mixed potential of the indicator electrode (IE) in a suspension and the IE potential placed in the separated eqs; and (2) the anomalous liquid junction potential of the RE placed in the suspension. It is not the consequence of a boundary potential between the sediment and its eqs in the suspension potentiometric cells as is stated in the current definition of the SE.

Within Part A the measured cell potentials for suspension potentiometric cells are interpreted and explained in detail. With some former disagreements among investigations clarified, a new unambiguous operational definition of the SE is presented in Part B. It is defined as the difference in cell potential for two suspension potentiometric cells, one with both electrodes in the separated eqs and the other with both electrodes in the sediment or suspension. This potential difference is the sum of the change in the IE potential and the change in the liquid junction potential of the RE, when the electrodes are used for measurement, once in the sediment of the suspension and then in its eqs.

www.iupac.org/publications/pac/2007/7901/7901x0067.html
www.iupac.org/publications/pac/2007/7901/7901x0081.html


Page last modified 10 July 2007.
Copyright © 2003-2007 International Union of Pure and Applied Chemistry.
Questions regarding the website, please contact edit.ci@iupac.org
Link to CI Home Page Link to IUPAC E-News Link to IUPAC Home Page