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Title: Guidelines for Improving the Lower Detection Limit of Ion-Selective Electrodes: A Systematic Approach

Abstract

Zero-current membrane fluxes are the principal source of bias that has prohibited researchers from obtaining true, thermodynamic selectivity coefficients for membrane-based ion selective electrodes (ISEs). They are also responsible for the mediocre detection limits historically seen with these types of potentiometric sensors. By choosing an experimental protocol that suppresses these fluxes, it becomes possible to obtain unbiased thermodynamic selectivity coefficients that are needed to produce ISEs with greatly improved detection limits. In this work, a Cs+-selective electrode based on calix[6]arene-hexaacetic acid hexaethyl ester (Cs I) is used to systematically demonstrate how unbiased selectivity coefficients can be obtained, and how they can be used to optimize inner filling solutions for low detection limit measurements. A comparison of biased selectivity methods (e.g., classical separate solution method (SSM), fixed interference method (FIM), matched potential method (MPM)) with the unbiased modified separate solution method (MSSM) found that selectivity coefficients were underestimated in several cases by more than 4 orders of magnitude. The importance of key experimental parameters, including diffusion coefficients and diffusion layer thicknesses in the aqueous and organic phases, on the minimization of ion fluxes and the improvement of lower detection limits is also described. A dramatic reduction of membrane fluxes by themore » covalent attachment of a Ca2+-selective ionophore to a methyl methacrylate-decyl methacrylate copolymer matrix is also demonstrated. The ionophore-immobilized ISE exhibited no super-Nernstian response and yielded a detection limit of 40 ppt with an inner filling solution of 1 x 10-3 M KCl. Finally, a set of guidelines for experimental protocols leading to obtaining unbiased selectivity coefficients and producing ISEs for trace level analyses is given.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
899145
Report Number(s):
PNNL-SA-51171
TRN: US0701741
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Electroanalysis, 19(2-3):144-154
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; COPOLYMERS; DIFFUSION; ELECTRODES; ESTERS; ION-SELECTIVE ELECTRODES; MEMBRANES; METHACRYLATES; MINIMIZATION; RECOMMENDATIONS; SENSITIVITY; THERMODYNAMICS; low detectioin limit; zero-current ion fluxes; ion-selective electrode

Citation Formats

Radu, Aleksandar, Peper, Shane M., Bakker, Eric, and Diamond, Dermot. Guidelines for Improving the Lower Detection Limit of Ion-Selective Electrodes: A Systematic Approach. United States: N. p., 2007. Web. doi:10.1002/elan.200603741.
Radu, Aleksandar, Peper, Shane M., Bakker, Eric, & Diamond, Dermot. Guidelines for Improving the Lower Detection Limit of Ion-Selective Electrodes: A Systematic Approach. United States. doi:10.1002/elan.200603741.
Radu, Aleksandar, Peper, Shane M., Bakker, Eric, and Diamond, Dermot. Mon . "Guidelines for Improving the Lower Detection Limit of Ion-Selective Electrodes: A Systematic Approach". United States. doi:10.1002/elan.200603741.
@article{osti_899145,
title = {Guidelines for Improving the Lower Detection Limit of Ion-Selective Electrodes: A Systematic Approach},
author = {Radu, Aleksandar and Peper, Shane M. and Bakker, Eric and Diamond, Dermot},
abstractNote = {Zero-current membrane fluxes are the principal source of bias that has prohibited researchers from obtaining true, thermodynamic selectivity coefficients for membrane-based ion selective electrodes (ISEs). They are also responsible for the mediocre detection limits historically seen with these types of potentiometric sensors. By choosing an experimental protocol that suppresses these fluxes, it becomes possible to obtain unbiased thermodynamic selectivity coefficients that are needed to produce ISEs with greatly improved detection limits. In this work, a Cs+-selective electrode based on calix[6]arene-hexaacetic acid hexaethyl ester (Cs I) is used to systematically demonstrate how unbiased selectivity coefficients can be obtained, and how they can be used to optimize inner filling solutions for low detection limit measurements. A comparison of biased selectivity methods (e.g., classical separate solution method (SSM), fixed interference method (FIM), matched potential method (MPM)) with the unbiased modified separate solution method (MSSM) found that selectivity coefficients were underestimated in several cases by more than 4 orders of magnitude. The importance of key experimental parameters, including diffusion coefficients and diffusion layer thicknesses in the aqueous and organic phases, on the minimization of ion fluxes and the improvement of lower detection limits is also described. A dramatic reduction of membrane fluxes by the covalent attachment of a Ca2+-selective ionophore to a methyl methacrylate-decyl methacrylate copolymer matrix is also demonstrated. The ionophore-immobilized ISE exhibited no super-Nernstian response and yielded a detection limit of 40 ppt with an inner filling solution of 1 x 10-3 M KCl. Finally, a set of guidelines for experimental protocols leading to obtaining unbiased selectivity coefficients and producing ISEs for trace level analyses is given.},
doi = {10.1002/elan.200603741},
journal = {Electroanalysis, 19(2-3):144-154},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}