Trace-Level Potentiometric Detection in the Presence of a High Electrolyte Background

Abstract

Polymeric membrane ion-selective electrodes (ISEs) have become attractive tools for trace-level environmental and biological measurements. However, applications of such ISEs are often limited to measurements with low levels of electrolyte background. This paper describes an asymmetric membrane rotating ISE configuration for trace-level potentiometric detection with a high-interfering background. The membrane electrode is conditioned in a solution of interfering ions (e.g., Na + ) so that no primary ions exist in the ISE membrane, thus avoiding the ion-exchange effect induced by high levels of interfering ones in the sample. When the electrode is in contact with the primary ions, the interfering ions in the membrane surface can be partially displaced by the primary ions due to the favorable ion−ligand interaction with the ionophore in the membrane, thus causing a steady-state potential response. By using the asymmetric membrane with an ion exchanger loaded on the membrane surface, the diffusion of the primary ions from the organic boundary layer into the bulk of the membrane can be effectively blocked; on the other hand, rotation of the membrane electrode dramatically reduces the diffusion layer thickness of the aqueous phase and significantly promotes the mass transfer of the primary ions to the sample−membrane interface. The induced accumulation of the primary ions in the membrane boundary layer largely enhances the nonequilibrium potential response. By using copper as a model, the new concept offers a subnanomolar detection limit for potentiometric measurements of heavy metals with a high electrolyte background of 0.5 M NaCl. S ince the discovery of lowering the detection limit of ionselective electrodes (ISEs) in 1997, 1 spectacular progress in the development and application of potentiometric sensors has been made, and the new wave of ISEs has already arrived. 2−4The lower detection limit of polymeric membrane ISEs has been improved by a factor of up to 10 6 , while the discrimination of interfering ions has even improved by a factor up to 10 10 . 5Nowadays, ISEs have evolved to be a promising technique for trace-level environmental and biological measurements. 6−9However, it should be noted that most of the applications of polymeric membrane-based ISEs developed so far are limited to measurements with low levels of electrolyte background, typically for drinking water 10,11 or well-controlled solutions. 8,9Very few polymeric membrane ISEs have been reported for potentiometric detection with a high-interfering background. The ISE with an optimal internal solution buffered for primary ions has been used for determination of low levels of calcium with an intracellular fluid background containing high concentrations of K + , Na + , and Mg 2+ . 12 To avoid super-or sub-Nernstian behavior, tedious optimization of the inner solution is required for each sample. By coupling the microliter potentiometric detection to an efficient online electrochemical accumulation step, solid-contact ion-selective microele...

A simple approach for fabricating solid-contact ion-selective electrodes using nanomaterials as transducers

“…The results are summarized in Table 1. It can be seen that the potentiometric selectivity coefficients of the proposed solid-contact electrode are comparable to those of the conventional liquid-contact electrode based on the same ionophore [34].…”

Pulsed Galvanostatic Control of a Polymeric Membrane Ion-Selective Electrode for Potentiometric Immunoassays

“…However, our previous studies indicate that there is no obvious sensitivity change of the asymmetric membrane electrode within 2 weeks. 29 Moreover, researchers have shown that the immunosensor based on the polymeric membrane exhibited satisfactory long-term stability and reliability. 30 2.6.…”

DNA Nanostructure-Based Magnetic Beads for Potentiometric Aptasensing

“…The potential responses were measured by a polycation-sensitive membrane electrode with a rotating electrode configuration (3000 rpm) as described before (see the Supporting Information). 11 Before measurements, the electrodes were conditioned in 0.01 M NaCl for 5 min to obtain a stable baseline.…”

“…9 However, most of the successful applications of ISEs are still limited to detection of a number of ionic species, and low levels of electrolyte backgrounds are usually required for the low detection limit measurements. 10,11 It thus remains a challenge to apply potentiometric sensors to detect a broad range of different molecular targets with high sensitivity, especially in complex media (e.g., clinical or environmental samples).…”