Tanji Yin

Potentiometric measurement of ascorbate by using a solvent polymeric membrane electrode

A novel potentiometric method for the determination of ascorbate is described in this communication. It is based on ascorbate oxidation with permanganate which is continuously released from the inner reference solution of a ligand-free tridodecylmethylammonium chloride (TDMAC)-based polymeric membrane ion selective electrode (ISE). The ISE potential determined by the activity of permanganate ions released at the sample-membrane phase boundary is increased with the consumption of permanganate. The proposed membrane electrode is useful for continuous and reversible detection of ascorbate at concentrations in 0.1M NaCl ranging from 1.0 x 10(-6) to 1.0 x 10(-3)M with a detection limit of 2.2 x 10(-7)M.

All-Solid-State Polymeric Membrane Ion-Selective Miniaturized Electrodes Based on a Nanoporous Gold Film as Solid Contact

A new type of all-solid-state polymeric membrane ion-selective electrodes (ISEs) is developed by using a nanoporous gold (NPG) film as solid contact. The NPG film is in situ formed on the surface of a gold wire electrode by the multicyclic electrochemical alloying/dealloying method. The characteristics of the NPG film, such as the large surface area, high double layer capacitance, and good conductivity, have been demonstrated by cyclic voltammetry and electrochemical impedance spectroscopy. The NPG film offers a well-defined interface between the electronic conductor and the ion-selective membrane. The NPG film-based all-solid-state K(+) ISE shows a stable Nernstian response within the concentration range from 10(-6) to 10(-2) M, and the detection limit is 4.0 × 10(-7) M. The proposed electrode exhibits an improved potential stability with a reduced water layer in comparison with the coated-wire K(+)-ISE, which is due to the bicontinuous electron- and ion-conducting properties of the ionophore-doped polymeric membrane/NPG film interlayer. Unlike the additionally coated intermediate layers as single-use solid contacts, the in situ formed NPG film as solid contact is reusable. This work provides a versatile method for fabricating the robust, reliable, and low-maintenance miniaturized ISEs.

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

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.

An all-solid-state polymeric membrane Pb2+-selective electrode with bimodal pore C-60 as solid contact

An all-solid-state polymeric membrane Pb(2+) ion-selective electrode (Pb(2+)-ISE) based on bimodal pore C60 (BP-C60) as solid contact has been developed. A BP-C60 film can be readily formed on the surface of a glassy carbon electrode by electrochemical deposition. Cyclic voltammetry and electrochemical impedance spectroscopy have been employed to characterize the BP-C60 film. The large double layer capacitance and fast charge-transfer capability make BP-C60 favorable to be used as solid contact for developing all-solid-state ISEs. The all-solid-state BP-C60-based Pb(2+)-ISE shows a Nernstian response in the range from 1.0×10(-9) to 1.0×10(-3)M with a detection limit of 5.0×10(-10)M. The membrane electrode not only displays an excellent potential stability with the absence of a water layer between the ion-selective membrane and the underlying BP-C60 solid contact, but also is insensitive to interferences from O2, CO2 and light. The proposed solid-contact Pb(2+)-ISE has been applied to determine Pb(2+) in real water samples and the results agree well with those obtained by anodic stripping voltammetry.

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

A simple and robust approach for the development of solid-state ion-selective electrodes (ISEs) using nanomaterials as solid contacts is described. The electrodes are fabricated by using the mixture of an ionic liquid (IL) and a nanomaterial as intermediate layer, formed by melting the IL. Tetradodecylammonium tetrakis(4-chlorophenyl)borate (ETH 500) is chosen as an model of IL to provide strong adhesion between the inner glassy carbon electrode and the intermediate layer. Nanomaterials including single-walled carbon nanotubes (SWCNTs) and graphene were used as active ion-to-electron transducers between the glassy carbon electrode and the ionophore-doped ISE membrane. By using the proposed approach, the solid-contact Cu(2+)- and Pb(2+)-selective electrodes based on ETH 500/SWCNTs and ETH 500/graphene as transducers, respectively, have been fabricated. The proposed electrodes show detection limits in the nanomolar range and exhibit a good response time and excellent stability.

Potentiometric Aptasensing of Vibrio alginolyticus Based on DNA Nanostructure-Modified Magnetic Beads

A potentiometric aptasensing assay that couples the DNA nanostructure-modified magnetic beads with a solid-contact polycation-sensitive membrane electrode for the detection of Vibrio alginolyticus is herein described. The DNA nanostructure-modified magnetic beads are used for amplification of the potential response and elimination of the interfering effect from a complex sample matrix. The solid-contact polycation-sensitive membrane electrode using protamine as an indicator is employed to chronopotentiometrically detect the change in the charge or DNA concentration on the magnetic beads, which is induced by the interaction between Vibrio alginolyticus and the aptamer on the DNA nanostructures. The present potentiometric aptasensing method shows a linear range of 10–100 CFU mL−1 with a detection limit of 10 CFU mL−1, and a good specificity for the detection of Vibrio alginolyticus. This proposed strategy can be used for the detection of other microorganisms by changing the aptamers in the DNA nanostructures.

An all-solid-state imprinted polymer-based potentiometric sensor for determination of bisphenol S

An all-solid-state polymeric membrane potentiometric sensor for determination of bisphenol S has been developed by using the imprinted polymer as the receptor and a nanoporous gold film as the solid contact. The sensor has a linear concentration range of 0.1 to 2 μM with a detection limit of 0.04 μM.