Sensitivity, electrodes for

H. Duessel, A. Dostal, and F. Scholz, Hexacyanoferrate-based composite ion-sensitive electrodes for voltammetry. Fresenius J. Anal. Chem. 355, 21—28 (1996). 

The electrodes modified by hexacyano-ferrates compounds were also used as voltammetric sensors [409-412]. The cadmium hexacyanoferrate-based composite ion-sensitive electrode for voltammetry was explored by Scholz and coworkers [409]. The potential of such electrode depends linearly on the logarithm of concentration of alkali and alkaline-earth metals ions in the solutions. Bo and fin have studied [410] Prussian blue (PB)/Pt modified electrode in GdGh electrolyte by cyclic voltammetry and in situ Fourier transform IR spectroscopy (FTIR) spectro-electrochemistry. Cadmium hexacyanofer-rates were formed on a PB film. 

H3. Hertz, C. H., and Siesjo, B., A rapid and sensitive electrode for continuous measurement of pC02 in liquids and tissue. Acta Physiol. Scand. 47, 115-123... 

Permeability of paint films to water, oxygen, and ions has been studied by many workers with a variety of methods including volumetric, gravimetric, and capacitance methods for water volumetric, barometric, and oxygen electrode based methods for oxygen and radioactive tracer, conductivity, and ion sensitive electrodes for ions (25. 41. 42 see also 14. 13. 43. and the references cited therein). 

Figure A3.14.5. Experimental records from Pt and Br -ion-sensitive electrode for the BZ reaction in batch showing regular oscillatory response.

Buschmann N, Schultz R (1993) Comparison of different ion-sensitive electrodes for the titrimetric determination of ionic surfactants. Toiside Surf Det 30 18-23... 

A microelectrode is an electrode with at least one dimension small enough that its properties are a fimction of size, typically with at least one dimension smaller than 50 pm [28, 29, 30, 31, 32 and 33]. If compared with electrodes employed in industrial-scale electrosynthesis or in laboratory-scale synthesis, where the characteristic dimensions can be of the order of metres and centimetres, respectively, or electrodes for voltannnetry with millimetre dimension, it is clear that the size of the electrodes can vary dramatically. This enonnous difference in size gives microelectrodes their unique properties of increased rate of mass transport, faster response and decreased reliance on the presence of a conducting medium. Over the past 15 years, microelectrodes have made a tremendous impact in electrochemistry. They have, for example, been used to improve the sensitivity of ASV in enviroiunental analysis, to investigate rapid... 

Luminescence has been used in conjunction with flow cells to detect electro-generated intennediates downstream of the electrode. The teclmique lends itself especially to the investigation of photoelectrochemical processes, since it can yield mfonnation about excited states of reactive species and their lifetimes. It has become an attractive detection method for various organic and inorganic compounds, and highly sensitive assays for several clinically important analytes such as oxalate, NADH, amino acids and various aliphatic and cyclic amines have been developed. It has also found use in microelectrode fundamental studies in low-dielectric-constant organic solvents. 

Meyerhoff, M. E. Fu, B. Bakker, E. et al. Polyion-Sensitive Membrane Electrodes for Biomedical Analysis, Anal. Chem. 1996, 68, 168A-175A. 

Methods of sulfate determination used in common practice suffer from essential disadvantages (time consumption, laboriousness, low sensitivity, etc.). For this reason, creation of sulfate-selective electrode suitable for direct potentiometric determination of this ion, has been attempted for a long time. Nowadays, nearly a dozen of sulfate-selective electrodes based on charged or neutral carriers of different stmcture have been described. Flowever, no known receptors for sulfate ions are available commercially. 

NEW COMPLEX CHALCOGENIDES AS SENSITIVE MATERIALS FOR ION SELECTIVE ELECTRODES... 

In the discussion of the relative acidity of carboxylic acids in Chapter 1, the thermodynamic acidity, expressed as the acid dissociation constant, was taken as the measure of acidity. It is straightforward to determine dissociation constants of such adds in aqueous solution by measurement of the titration curve with a pH-sensitive electrode (pH meter). Determination of the acidity of carbon acids is more difficult. Because most are very weak acids, very strong bases are required to cause deprotonation. Water and alcohols are far more acidic than most hydrocarbons and are unsuitable solvents for generation of hydrocarbon anions. Any strong base will deprotonate the solvent rather than the hydrocarbon. For synthetic purposes, aprotic solvents such as ether, tetrahydrofuran (THF), and dimethoxyethane (DME) are used, but for equilibrium measurements solvents that promote dissociation of ion pairs and ion clusters are preferred. Weakly acidic solvents such as DMSO and cyclohexylamine are used in the preparation of strongly basic carbanions. The high polarity and cation-solvating ability of DMSO facilitate dissociation... 

In practical terms, it is suggested that, in any application where the presence of halide ions may cause problems, the concentration of these be monitored to ensure the purity of the liquids. This may be achieved either by the use of an ion-sensitive electrode, or alternatively by use of a chemical method such as the Vollhard procedure for chloride ions [52]. Seddon et al. have reported that effectively identical results were obtained with either method [37]. 

Sampling points for analysis should be planned in order to give the whole record of analysis, e.g. in oil production from the well via processing facilities to the export facilities. Correlation with plant parameters such as temperatures, pressures, flow rates and, stream compositions can provide valuable records. Emphasis on chemical analysis should be incorporated in the design of process plant. Automatic analysis systems especially those using ion-sensitive electrodes with recording of data are recommended. 

As early as 1937, Kolthoff and Sanders32) used silver halide discs as ion-sensitive membranes for the corresponding anion. They found that interferences through redox-systems were negligible with those membranes compared to electrodes of... 

The sensor is an ammonium ion-selective electrode surrounded by a gel impregnated with the enzyme mease (Figme 6-11) (22). The generated ammonium ions are detected after 30-60 s to reach a steady-state potential. Alternately, the changes in the proton concentration can be probed with glass pH or other pH-sensitive electrodes. As expected for potentiometric probes, the potential is a linear function of the logarithm of the urea concentration in the sample solution. 

Organic dyes, aside from their role as sensitization agents for wide band gap semiconductors have been employed also for stabilization of narrow band gap semiconductors. The majority of such studies have considered metal or metal-free phthalocyanine films for both sensitization and electrode protection purposes [35]. 

In selecting reference electrodes for practical use, one should apply two criteria that of reducing the diffusion potentials and that of a lack of interference of RE components with the system being studied. Thus, mercury-containing REs (calomel or mercury-mercuric oxide) are inappropriate for measurements in conjunction with platinum electrodes, since the mercury ions readily poison platinum surfaces. Calomel REs are also inappropriate for systems sensitive to chloride ions. 

According to Eq. (12.8), the faradaic current is proportional to the square root of scan rate v. According to Eq. (12.13), however, the charging current is proportional to the scan rate. Thus, the ratio decreases with increasing v, and the measuring sensitivity falls. For this reason, relatively low scan rates, 20 to 50 mV/s, are used in measurements at solid electrodes. 

The sensitizers display a crucial role in harvesting of sunlight. To trap solar radiation efficiently in the visible and the near IR region of the solar spectrum requires engineering of sensitizers at a molecular level (see Section 9.16.3).26 The electrochemical and photophysical properties of the ground and the excited states of the sensitizer have a significant influence on the charge transfer (CT) dynamics at the semiconductor interface (see Section 9.16.4). The open-circuit potential of the cell depends on the redox couple, which shuttles between the sensitizer and the counter electrode (for details see Section 9.16.5). 

The partial oxygen pressure, p02, is particularly significant in metabolic processes of cells, and its variation from normal values often indicates pathologies (ischemic diseases, strokes, tumors). Accurate and localized measurements of the oxygen concentration are also desirable for differentiation between venous and arterial blood, or for cerebral mapping of task activation. In the past, invasive methods were used involving oxygen-sensitive electrodes which had to be placed directly in the blood or tissue and could only offer p02 from a few body points. 

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