27 No. 4
Guidelines for Potentiometric Measurements in Suspensions
This project aims to unambiguously define and interpret the suspension effect (SE) on the basis of recent experiments. It will take into account the enormous amount of theoretical and experimental work accomplished in 75 years since the term was first introduced—a period in which no consensus was achieved. On the basis of the recommended definition and interpretation, the significance of potentiometric measurements in suspensions performed in different ways will be explained.
The SE is defined as the difference of the galvanic cell voltage measured with the electrodes (i) in the equilibrium solution of the suspension and (ii) in its sediment. It will be argued that the SE should be regarded as the sum of two effects that occur when the electrodes are immersed in a suspension. These are (i) the transition of the indicator electrode from a reversible potential to an irreversible mixed potential, and (ii) a systematic error of measurement caused by the outflow of the solution from the reference electrode salt bridge into the suspension.
Due to the irreversible mixed potential of the indicator electrode, which cannot be eliminated in suspension measurements, no thermodynamically exact data can be obtained. Guidelines will be presented for modifications of potentiometric methods applied to suspensions and the significance of these measurements will be interpreted and illustrated.
For more information and comments, contact the Task Group Chairman S.F. Oman <[email protected]>.
last modified 6 June 2005.
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