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Chemistry International
Vol. 24, No. 6
November 2002


IUPAC Projects

Performance Evaluation Criteria for Preparation and Measurement of Macro- and Microfabricated Ion-Selective Electrodes

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 ionophorebased liquid membrane ion-selective electrodes (ISEs) has now entered the arena of trace analysis and precision science due to the latest updated and upgraded research and development 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 and Applied Chemistry 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 are of the same importance. Items we will discuss include the following:

  • conditioning of the multilayered 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 storage in humid atmosphere
  • conditioning and calibration before and after the measurement
  • effect of osmotic pressure (give a procedure, how to measure)
  • shelve and use lifetime (effect of storage); estimation of the residual lifetime 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.

For more information, contact the Task Group Chairman Yoshio Umezawa <[email protected]>.



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