Number: 2004-016-2-500
Title: Guidelines for potentiometric measurements in suspensions
Task Group
Chairman: S.F. Oman
Members: Filomena
Camões, Raj
Rajagopalan, and Petra
Spitzer
Completion Date: 2007 - project completed
Objective:
A) To state the causes and natures of the Suspension Effect in
potentiometric measurements in suspensions
B) On the base of A) to (i) give an unambiguous, experimentally
verified definition and interpretation of the Suspension Effect and
(ii)
recommend procedures for pH (pIon) measurements in suspensions
Description:
The term "suspension effect" (SE) was introduced seventy five
years ago. Originally it was defined as the difference between the potentiometrically
determined hydrogen ion concentration of a suspension and of the medium
pertaining to it. Many interpretations of this difference were published
until now but no consensus about its origin or explanation was accepted,
though an enormous experimental and theoretical study of these problems
was done. For the present it is possible to find two different definitions
even on the web sites of IUPAC. On the base of an early SE definition
and using a detailed analysis of the suspension galvanic cells the cause
and the nature of the SE phenomena can be explained and an unambiguous
definition of SE proposed.
One of the current definitions states the SE as "the difference
in emf obtained in the conventional determination of the pH in a suspension
and in its equilibrium solution" (Overbeek, 1953.) This is the
base of the new revised definition. This will be in accordance with
the "IUPAC Recommendations 2002" (on pH) and interpreted with
regard to its causes and natures.
Taking into account the revised definition and its interpretation,
described above, guidelines for practical routine pH (and pIon) measurements
in suspensions will be given. The electrodes and the instructions for
their use will be described and illustrated with some examples.
Progress:
April 2006 - A manuscript is being prepared for publication
in Pure Appl. Chem. A final document is submitted to public review
comments until 30 Sep 2006. > see provisional
recommendations
Jan 2007 - Project completed
Both a technical report and recommendatiosn have published been:
Guidelines for potentiometric measurements in suspensions
Part A. The suspension effect (IUPAC Technical Report)
Pure Appl.
Chem. 79(1),
67-79, 2007
Part B. Guidelines for practical pH measurements in soil suspensions
(IUPAC Recommendations 2006)
Pure Appl.
Chem.
79(1), 81-86, 2007
Last Update: 9 January 2007
<project announcement published in
Chem.
Int. Jul-Aug
2005 >