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Analytical Chemistry Division (V)

Number: 2002-003-2-500

Title: Performance evaluation criteria for preparation and measurement of macro and microfabricated ion-selective electrodes

Task Group
Yoshio Umezawa

Member: Erno Lindner

Completion Date: 2008 - project completed

During the past several years, the application of microfabrication technologies of practical microsensor devices has entered the field of biology and medicine and is beginning to serve as the driving force for discoveries in cell biology, neurobiology, pharmacology, and tissue engineering. In parallel, the methodology of ionophore based liquid membrane ISEs has now entered the arena of trace analysis and precision science due to the latest updated and upgraded R/D of this method. This circumstance has made it necessary to also upgrade and update the evaluation criteria for the preparation and measurements of ISEs, primarily microfabricated ISEs and potentiometric cells. This is in fact the purpose of this project.

There are more or less generally accepted evaluation criteria for ISEs. Some of those are summarized in Pure Appl. Chem. documents (PAC 1994, 66, 2527; PAC 1995; 67, 507).

In this new document, we will deal with the specialities of macro- and microfabricated ISE sensors; standard procedures for the microfabricated devices are much more critical compared to macroelectrodes. In addition, some evaluation criteria for the micro reference electrodes is of the same importance. Items we will discuss includes

  • Conditioning of the multi-layered sensor system (sensing membrane, underlying hydrogel and eventually biocompatible coating) before use to reach high stability readings, due to water transport through the membrane
  • Conditioning overnight or store in humid atmosphere. Conditioning and calibration before and after the measurement
  • Effect of osmotic pressure (give a procedure, how to measure)
  • Shelf and use life time (effect of storage); estimation of the residual life time in vivo and in vitro
  • Added-site optimization for selectivity and as requisite for Nernstian response
  • Electrode construction including microfabrication, FET covered with membranes, and Ppy electrode covered with membranes
  • Response time as well as detection limit
  • Microfabricated inner and outer reference electrodes

We will correct the inconsistencies in the previous document (PAC 1994; 66, 2527), e.g., the definition of the calibration plot, which contradicts the convention related to the determination of pH. Finally, we will discuss the latest results concerning the lower detection limit, true selectivity coefficients and twice Nernstian slopes etc.

The darft report includes: 1. Introduction, 2. Ionophore based liquid membrane ion-selective electrodes, 3. Trace analysis with ion-selective electrodes, 4. Consequences of improved detection on limits on the selectivity coefficients, 5. Conditioning of ion selective electrodes for optimal performance, and 6. Inconsistencies in the recommended procedures for presenting a calibration plot for pH
and other ion selective electrodes.

The manuscript is 70% completed, and it is projected that the document will be ready for external review around March 2005.
> Nov 2004 report update (pdf file - 12KB)

> May 2006 report update (pdf file - 11KB)

> June 2007- Manuscript completed; minor revisions are necessary.

> Jan 2008 - Project completed - IUPAC Technical report published in Pure Appl. Chem. 80(1), 85-104, 2008.

Last Update: 15 January 2008

<project announcement published in Chem. Int. 24(6) 2002>

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Page last modified 15 January 2008.
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