Fluoride-selective electrode with internal redox reference electrode

The potential response of a symmetrical configuration in which the LaF₃-membrance is placed between two solutions is discussed. The electrode body provides contact with the inner surface of the fluoride membrane, with a solution containing Fe(CN) ₆ ^3– -Fe(CN) ₆ ^4– redox couple and a Pt wire as internal reference electrode. The electrode was examined in terms of potentialconcentration curves and potential-time response and shown to behave similarly to the commencal Orion fluoride electrode. The advantage of the proposed redox reference system is that the electrode has minimal drift immediately after assembly.     

Dodecyl benzene sulfonate anion-selective electrode based on polyaniline-coated electrode

A new dodecyl benzene sulfonate (DBS⁻) ion-selective electrode based on polyaniline is reported. The films of polyaniline doped with DBS⁻ were prepared electrochemically on platinum electrodes in the solution containing 1.0×10⁻³ M aniline and 7.0×10⁻³ M DBS⁻. The optimum potentiometric response was obtained for prepared polymeric film by passing electricity of 7.5 C cm⁻². The electrode exhibits an excellent Nernstian slope of −59.1±0.3 mV per decade for DBS⁻ ion over a wide concentration range (5.0×10⁻⁶ to 4.1×10⁻³ M) with a low detection limit (1.0×10⁻⁶ M). The proposed electrode revealed good sensitivities for DBS⁻ ion over a wide variety of other anions and can be used in the wide pH range of 5-10. It shows good stability, good reproducibility, wide range of pH independency and fast response (<20 s) without using internal solution. This electrode could be used for the determination of DBS⁻ in the real samples.     

Behaviour of the platinum electrode as a pH electrode

The platinum wire electrode behaves as a good pH electrode in the titration of 1.0 and 0.1N sulphuric or hydrochloric acid with the equivalent concentration of sodium hydroxide. The efficiency is greater when sulphuric acid is used. The end-points obtained are very close to those obtained with a glass-calomel system.     

Amperometric aspartate electrode

An amperometric enzyme electrode for L-aspartate determination was developed. The probe consisted of a platinum electrode which senses hydrogen peroxide produced from the reactions catalyzed by two enzymes co-immobilized on a preactivated polymeric membrane, α-Ketoglutarate in the presence of L-aspartate was transaminated to L-glutamate by aspartate aminotransferase and the glutamate produced was oxidized by glutamate oxidase, with concomitant production of hydrogen peroxide. Additional protective membranes eliminated interferences from glutamate and most electroactive compounds. The response curve of the probe was linear over the concentration range 1.0 × 10^?6 M to 2.0 × 10^?4 M aspartate and was useful for at least two months. Aspartic acid in some pharmaceutical products was determined and the results correlated well with a liquid chromatographic reference method and the manufacturer's specification.     

Polyferredoxin-based electrode materials

Electrochemical oxidation of the hydrosulfide cluster [Fe4S4(SH)4]2- on gold, platinum or vitreous carbon in a methyl cyanide electrolyte leads to the growth of a conducting film. Spectroscopic and other evidence suggests that the film has cubane centres, predominately in the [4Fe4S]3+ oxidation state, which are linked by disulfide ligands to give an anionic array of [Fe4S4(S approximately)4]n- units. X-ray data suggests some long-range order in the electrode material. The polyferredoxin binds redox active cations consistent with an anionic array.     

Trifluoroacetate ion-selective electrode

The trifluoroacetate ion-selective electrode was prepared by using the organic solvent solution of trifluoroacetate salt of crystal violet or tris(bathophenanthroline) iron(II) chelate.The response is linear over the activity range 10^?1 to 3 × 10^?5M, with a Nernstian slope 60 mV/activity decade at 29 °C. The interferences of divalent ions, chloride, fluoride and acetate ions are extremely low. Iodide interferes greatly.     

Monohydrogenphosphate-sensing electrode formulations

Four-component Ag₂S:PbS:PbHPO₄: Ag₂HPO₄ and three-component Ag₂S:PbS:PbHPO₄ formulations have been prepared and evaluated for sensitivity to monohydrogenphosphate. The 3:1:1 composition is superior in terms of ease of preparation, stability, rapidity of response and reproducibility. Testing was done over the range 10^-1–10^-5 M HPO₄^2- in buffer at pH 8.44 with constant ionic strength. Response times to 64% of final values varied between 60 and 300 s depending upon concentration, and potential changes with concentration varied between 25 and 31.5 mV/decade in the 10^-1–10^-3 M range, depending upon electrode configuration. Many common ions interfere.     

Floating electrode dielectrophoresis

In practice, dielectrophoresis (DEP) devices are based on micropatterned electrodes. When subjected to applied voltages, the electrodes generate nonuniform electric fields that are necessary for the DEP manipulation of particles. In this study, electrically floating electrodes are used in DEP devices. It is demonstrated that effective DEP forces can be achieved by using floating electrodes. Additionally, DEP forces generated by floating electrodes are different from DEP forces generated by excited electrodes. The floating electrodes' capabilities are explained theoretically by calculating the electric field gradients and demonstrated experimentally by using test-devices. The test-devices show that floating electrodes can be used to collect erythrocytes (red blood cells). DEP devices which contain many floating electrodes ought to have fewer connections to external signal sources. Therefore, the use of floating electrodes may considerably facilitate the fabrication and operation of DEP devices. It can also reduce device dimensions. However, the key point is that DEP devices can integrate excited electrodes fabricated by microtechnology processes and floating electrodes fabricated by nanotechnology processes. Such integration is expected to promote the use of DEP devices in the manipulation of nanoparticles.     

The parathiocyanogen electrode

Stable, yellow anodic films of parathiocyanogen (SCN) _x were formed on a platinum electrode from 2.8 M KSCN in methanol at 45 °C at a constant current of 20–40 mA cm⁻² for 15–30 min. Loosely bound orange crystals of a more amorphous character were removed by rinsing to leave an adherent yellow film with sharp Raman bands under 647.1 nm laser excitation at 627 cm⁻¹ (vCS), 1152 cm⁻¹ and 1236–1261 cm⁻¹ (vNN and vCN). The lack of electroactivity and short-lived photocurrents pointed to an insulating film at potentials up to 1.0 V (SHE). At more positive potentials, longer-lasting photocurrents were obtained, consistent with breakdown of the insulating film. XPS scans confirmed N:C:S ratios close to 1:1:1, with a deficiency of S of some 10% due to S lost as sulfate at the film surface. Oxidation of SeCN⁻ in neutral aqueous solution led to the formation of a less-stable orange paraselenocyanogen film with a Raman band at 1256–1267 cm⁻¹, which decomposed within a day to grey selenium. Received: 12 December 1997 / Accepted: 23 March 1998     

Simulations of cyclic voltammetric and chronoamperometric electrode responses at a disk electrode using combinations of spherical and cylindrical electrode geometries

Using geometric models based on one-dimensional transport at spheres and cylinders, three methods for improving the simulation of voltammetric behavior of a disk electrode have been explored. One method is based on the common assumption of equivalency between the limiting currents for a disk and a hemisphere under steady-state diffusion conditions. The second method involves the use of a partial-sphere geometry which is a better approximation that is suitable at the extreme diffusional limits achievable at a disk electrode of fully planar and steady-state transport. The third method, which is generally applicable, is a further refinement that uses a combination of appropriate one-dimensional spherical and cylindrical geometries. The results demonstrate that reasonably accurate approximations of disk behavior for several reaction mechanisms can be achieved in a fraction of the time required to compute the more rigorous two-dimensional model. We propose that the approximation serve primarily as a fast way to explore system behavior and establish approximate values of the relevant parameters. More accurate computations can then be performed using the two-dimensional model.     

Immobilization of enzyme to platinum electrode and its use as enzyme electrode

A glucose electrode was fabricated by immobilizing glucose oxidase covalently onto a platinized platinum electrode. The sensor showed rapid response with response time of 2—4 s, and also the linear response to the glucose concentration, ranging from 2 x 10^-3 to 5 mM. The sensitivity was found to be correlated with the surface area of a base electrode used.     

Determination of surface potentials from the electrode potentials of a single-crystal electrode

Determination of surface potentials Psi0 at the metal oxide/aqueous solution interface from measured electrode potentials of a metal oxide single-crystal electrode (SCrE) is described. The proposed method is based on the surface complexation model and evaluates the surface potential at the isoelectric point, i.e., at pHiep. This value is used for calculation of Psi0 values from the measured electrode potentials. Both 1-pK and 2-pK models produced the same result so that the procedure does not depend on the assumed mechanism of the surface charging. It is proposed to determine the pristine point of zero charge pHeln and the isoelectric point pHiep, and use these data to set the scale of surface potentials. The value of pHeln can be obtained at a sufficiently low ionic strength where pHpzc coincides with pHiep. The method is demonstrated on the example of the anatase single-crystal electrode. From the shifts of pHiep and pHpzc with respect to the pristine point of zero charge pHeln it was concluded that Cl- ions exhibit higher affinity for association with positively charged surface groups than ClO-4 ions. Also, preferential surface association of Na+ cations compared to both anions was detected. The slopes of the Psi0(pH) functions were found to be significantly lower in magnitude with respect to the Nernst equation, which is due to the high degree of counterion association at the surface caused by their relatively high concentration.     

Tungsten electrode for urea

Tungsten electrodes for urea were prepared via covalent linking of urease on oxidized metal surfaces in different ways. The most stable electrodes were obtained when tungsten was silanized and activated by glutaraldehyde or hexamethylene diisocyanate. The electrode with urease coupled via glutaraldehyde was tested for optimum conditions of use. The nature of the buffer and its concentration and ionic strength are particularly important.     

Effect of electrode membrane surface ratio and thickness on lead electrode potential

Summary The lead ion selective electrode (ISE) consisting of PbS-Ag₂S is normally used with a membrane surface of outer layer areaA _o) and inner layer area (A _i) at unity (A _o=A _i). Partial covering of one surface area with an insulating material and keeping the other surface layer intact resulted in different ratios of membrane surface areas exposed to lead solutions. The potential linearly increased with increasing theA _o/A _i ratio and decreased with decreasing theA _o/A _i ratio. The lead ISE potential increased linearly with increasing the membrane thickness, but which required much longer time for a stable potential.

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Wirkung von Oberflächenverhältnis und Dicke der Elektrodenmembran auf das Potential einer Bleielektrode

Zusammenfassung Die aus PbS-Ag₂S bestehende spezifische Bleiionen-Elektrode wird üblicherweise mit einem Oberflächenverhältnis der Außenfläche (A _o) und der Innenfläche (A _i) mitA _o=A _i verwendet. Durch teilweise Abdeckung einer Oberfläche mit isolierendem Material, ohne daß die andere Oberfläche verändert wird, ergaben sich verschiedene Verhältnisse der mit der Bleilösung in Berührung stehenden Oberflächen. Mit dem VerhältnisA _o/A _i stieg das Potential linear an bzw. es fiel mit diesem Verhältnis ab. Das Potential der spezifischen Bleielektrode stieg mit der Dicke der Membran, stabilisierte sich aber wesentlich langsamer.

     

Bienzyme amperometric lactate-specific electrode

The electrode, based on a lactate dehydrogenase and a diaphorase, permits the assay of l-lactate in the concentration range 0.2–8 mM with a response time of about 40 s. Both the enzymes are commercially available. The amperometric detection of hexacyanoferrate(II) at a platinum electrode is done at 0.3 V (vs. SCE) instead of 0.8 V as in the detection of NADH, improving the selectivity of the sensor.