Voltammetric sizing of inert particles.

The average size of inert particles is determined using a simple electrochemical procedure. Alumina particles are deposited on an edge-plane graphite electrode, and a cyclic voltammogram is recorded. The scan rate employed varies between 0.2 and 2 V s(-1). At these scan rates the diffusion layer thickness is greater than the size of the alumina particles, minimizing the influence of the particles' height on the observed voltammetry. The average size of the particles is determined via comparison of the experimental voltammograms with simulations.     

Role of carbonyl sites in the electrochemical response of 2,6-diaminopurin-8-ol

Modified graphite electrodes were prepared with materials containing carbonyl functional groups, including polypyrrole containing poly(methyl vinyl ketone). The effect of the modification on the electrochemical response of 2,6-diaminopurin-8-ol, a small, electrochemically fast biological molecule with primary amine groups which absorbs on active graphite, was evaluated. The results show that the chemical interactions between 2,6-diaminopurin-8-ol and the surface carbonyl functional groups do not by themselves contribute to the reactivity of the probe molecule.     

Differential ion-selective membrane electrode-based potentiometric gas-sensing cells with enhanced gas sensitivity

A novel design for devising static and automated flow-through type potentiometric gas-sensing systems with enhanced response slopes is described. The approach involves the use of two working gas-sensing electrode half-cells in a differential measurement arrangement. One of the half-cells employs a pH-sensitive polymeric membrane electrode to sense pH changes from diffusing analyte gas within a suitable inner electrolyte solution housed behind an outer gas-permeable membrane. The second working half-cell is fabricated with an anion- or cation-selective membrane electrode that responds selectively to the conjugate acid or base ionic form of the analyte gas trapped within an inner buffer solution housed behind a similar gas-permeable membrane. When the two internal solutions of the half-cells are in electrolytic contact, the differential response of the resulting gas-sensing scheme is significantly enhanced compared with the response of a conventional single working electrode/reference electrode type gas cell. For the model analyte gas ammonia, response slopes observed for both static and flow-through measurement schemes approach the 118 mV decade^?1 predicted by theory. To demonstrate its analytical utility, the flow-through arrangement was used to determine ammonia-N concentrations in bioreactor media with good correlation with conventional electrode and enzymatic methods. The prospects of fabricating similar differential detection arrangements for CO₂, NO₂ and SO₂ are discussed.     

A higher conductivity Bi2O3-based electrolyte

We have developed a Bi₂O₃ electrolyte doped with Dy₂O₃ and WO₃ (DyWSB) that exhibits a higher conductivity than that of 20 mol% erbia stabilized bismuth oxide (20ESB), thus, giving it the highest conductivity of any known solid oxide electrolyte. Electrical conductivity results of the Dy–W stabilized bismuth oxide system are presented. The dopants were selected based on their polarizability and its effect on structural stability and conductivity. At 800 °C, the conductivity of (BiO_1.5)_0.88(DyO_1.5)_0.08(WO₃)_0.04 is 0.57 S/cm (1.5 times as high as that of 20ESB), and at 500 °C, the conductivity is 0.043 S/cm (2 times as high as that of 20ESB).     

Modified carbon-containing electrodes in stripping voltammetry of metals. Part II. Composite and microelectrodes

The second part of the review, which covers modified carbon-containing electrodes, describes composite and microelectrodes. Electrodes made of commercial and laboratory carbon-containing composite materials are discussed. Impregnated and thick-film electrodes and microelectrodes made of carbon fibers form a separate group. Various modifiers and methods of electrode modification are presented. Prospects for the future development of solid-state modified electrodes are considered.     

Disposable electrochemical flow cells for catalytic adsorptive stripping voltammetry (CAdSV) at a bismuth film electrode (BiFE)

Catalytic adsorptive stripping voltammetry (CAdSV) has been demonstrated at a bismuth film electrode (BiFE) in an injection-moulded electrochemical micro-flow cell. The polystyrene three-electrode flow cell was fabricated with electrodes moulded from a conducting grade of polystyrene containing 40% carbon fibre, one of which was precoated with Ag to enable its use as an on-chip Ag/AgCl reference electrode. CAdSV of Co(II) and Ni(II) in the presence of dimethylglyoxime (DMG) with nitrite employed as the catalyst was performed in order to assess the performance of the flow cell with an in-line plated BiFE. The injection-moulded electrodes were found to be suitable substrates for the formation of BiFEs. Key parameters such as the plating solution matrix, plating flow rate, analysis flow rate, solution composition and square-wave parameters have been characterised and optimal conditions selected for successful and rapid analysis of Co(II) and Ni(II) at the ppb level. The analytical response was linear over the range 1 to 20 ppb and deoxygenation of the sample solution was not required. The successful coupling of a microfluidic flow cell with a BiFE, thereby forming a “mercury-free” AdSV flow analysis sensor, shows promise for industrial and in-the-field applications where inexpensive, compact, and robust instrumentation capable of low-volume analysis is required.     

Syntheses and structural characterization of two new nanostructured Bi(III) supramolecular polymers via sonochemical method

Two new bismuth(III) coordination supramolecular polymers, {[Bi₂(Hbpp)(bpp)(μ-I)₂I₆](Hbpp)·MeOH}_n (1) and [Bi(Hbpp)(Br₄)] (2), (bpp = 1,3-di(pyridin-4-yl)propane) were prepared and were structurally characterized by single crystal X-ray diffraction. Single crystalline one-dimensional materials were prepared using a heat gradient applied a solution of the reagents using the branched tube method. The structural determination by single crystal X-ray crystallography shows that compounds 1 and 2 form monoclinic polymers with symmetry space group P2₁ in the solid state. These new nanostructured Bi(III) supramolecular compounds, {[Bi₂(Hbpp)(bpp)(μ-I)₂I₆](Hbpp)·MeOH} (1) and [Bi(Hbpp)(Br₄)] (2), were also synthesized by sonochemical method. The nanostructures were characterized by Field Emission-scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD) and IR spectroscopy.