Voltammetric ion-selective electrodes

Controlled potential methods have been successfully applied to ion-selective electrodes. The term voltammetric ion-selective electrode (VISE) was suggested by Cammann [60], Senda and coworkers called electrodes placed under constant potential conditions amperometric ion-selective electrodes (AISE) [61, 62], Similarly to controlled current methods potentiostatic techniques help to overcome two major drawbacks of classic potentiometry. First, ISEs have a logarithmic response function, which makes them less sensitive to the small change in activity of the detected analyte. Second, an increased charge of the detected ions leads to the reduction of the response slope and, therefore, to the loss of sensitivity, especially in the case of large polyionic molecules. Due to the underlying response mechanism voltammetric ISEs yield a linear response function that is not as sensitive to the charge of the ion. 

D. Henn and K. Cammann, Voltammetric ion-selective electrodes (VISE). Electroanalysis 12, 1263— 1271 (2000). 

Scanning Electron Microscopy and X-Ray Microanalysis Principles of Electroanalytical Methods Potentiometry and Ion Selective Electrodes Polarography and Other Voltammetric Methods Radiochemical Methods Clinical Specimens Diagnostic Enzymology Quantitative Bioassay... 

Detection of Li+ in artificial serum with a voltammetric Li-selective electrode in a flowthrough system was demonstrated [64], Lithium salts such as lithium carbonate have been extensively used for treatment of manic depressive and hyperthyroidism disorders. The therapeutic range of Li concentration is generally accepted to be 0.5-1.5mM in blood serum. The authors used normal pulse voltammetry in which a stripping potential was applied between pulses in order to renew the membrane surface and expel all of the extracted ions from the membrane, similar to galvanostatically controlled potentiometric sensors described above. Unfortunately, the insufficient selectivity... 

M. Senda, H. Katano, and M. Yamada, Amperometric ion-selective electrode. Voltammetric theory and analytical applications at high concentration and trace levels. J. Electroanal. Chem. 468, 34-41 (1999). 

There is no perfect way to distinguish between what is conceptually dissolved and what is non-dissolved (particulate). Ion-selective electrodes respond selectively to solute ions but are often not sufficiently selective. One other possibility is to use voltammetric techniques on Hg (or other) electrodes in presence of colloids without prior centrifugation or filtration. Gongalves et al. (1985, 1987), Muller and Sigg (1990) (cf. Chapter 11.3). 

Figure 5.7 shows a typical application of gas-diffusion membranes isolation of the circulating sample from a voltammetric or potentiometric electrode for the electrochemical determination of gaseous species. The ion-selective electrode depicted in this Figure includes a polymer membrane containing nonactin that is used for the potentiometric determination of ammonia produced in biocatalytic reactions. Interferences from alkali metal ions are overcome by covering the nonactin membrane with an outer hydro-... 

Chapters 1 to 5 deal with ionophore-based potentiometric sensors or ion-selective electrodes (ISEs). Chapters 6 to 11 cover voltammetric sensors and biosensors and their various applications. The third section (Chapter 12) is dedicated to gas analysis. Chapters 13 to 17 deal with enzyme based sensors. Chapters 18 to 22 are dedicated to immuno-sensors and genosensors. Chapters 23 to 29 cover thick and thin film based sensors and the final section (Chapters 30 to 38) is focused on novel trends in electrochemical sensor technologies based on electronic tongues, micro and nanotechnologies, nanomaterials, etc. 

Electro-analytical techniques have been used extensively in studies of natural waters. For example, ion-selective electrodes allow measurement of the activity of free hydrated ions in solution (species highly relevant in toxicity studies) and voltammetric methods (polarography and ASV) exhibit a high degree of selectivity (for highly labile species). Electro-chemical techniques also facilitate identification of the valency state of elements such as Fe, Cr, Tl, Sn, Mn, Sb, As, Se, Y U and I. For several other elements only one state is electro-chemically active, and redox state speciation becomes a special case of labile/inert species discrimination. The toxicity of an ion can vary with valency, for example, Cr is more toxic than Crm, while for As, Sb and Tl, the lower valency form is more toxic. 

Most of the analytes (pC02, Na , K, Ca , and pH) are determined by potentiometric measurements using membrane-based ion-selective electrode technology. The hematocrit is measured by electrolytic conductivity detection, and p02 is determined with a Clark voltammetric sensor (see Section 23B-4). Other results are calculated from these data. 

Potentiometric ion-selective electrodes are passive probes, which in contrast to voltammetric sensors do not convert the analyte in the sample. The response of an ISE depends linearly on the logarithm of the activity (concentration) of a potential determining ion (primary ion) in the presence of other ions. The schematic layout of a complete potentiometric cell including an ion-selective electrode is shown in Figure 2. The electrochemical notation of the cell assembly is given as ... 

Ion-selective electrodes with tip diameters in the range of 0.5 to 10 pm have been developed for ions such as potassium, calcium, and chloride, and these have been used to study the distribution of these ions in both the extra- and intra-cellular fluid. These electrodes are used in the potentiometric mode, and the specificity is established by using a selective membrane that is only permeable to the ion of interest. Voltammetric techniques have also been useful for in vivo measurements the most widely used is the oxygen electrode, which incorporates a polymer film that is only permeable to oxygen. 

Electrochemical instruments are normally based on the changes in electrical energy that occur when a chemical reaction takes place, for example ion-selective electrodes (potentiometry) and voltammetric techniques. These can be measured in different ways and can give various qualitative and quantitative information about the reactants or products. In the case of conductivity measurements, changes in ionic content are monitored and, although nonspecific, can give useful data. 

The use of FIA is not limited to optical sensors. It has been previously used to test ion selective electrodes [12, 68], and most recently to testing in the development of pneumatic gas voltammetric detectors [1050, 1051]. Also the surface treatment of glassy carbon electrodes has been evaluated by means of their voltammetric response observed in the FIA mode [853]. 

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