Polarography selectivity

When either pulse polarography or anodic stripping voltammetry can be used, the selection is often based on the analyte s expected concentration and the desired... 

Although the speciation of some minor elements has been determined directly by experimental means (e.g., ion selective electrodes, polarography, electron spin resonance) most of our thinking about speciation is based on equilibrium calculations. Garrels and Thompson... 

Under optimum conditions LPS voltammetry is an order of magnitude more sensitive than polarography (i.e., the detection limit is about 10 M). As in classical polarography, somewhat higher sensitivity and selectivity can be attained when using a differential version (i.e., when recording, as a function of potential, not the current but its derivative with respect to potential). 

Electrochemistry voltammetry, anodic stripping (ASV), cathodic stripping (CSV), polarography, differential pulse polarography (DPP), ion selective electrode (ISE)... 

A hanging electrolyte drop has also been applied to determine ionic species in solution using differential-pulse-stripping voltammetry procedures [69]. Particular emphasis was given to assessing the selectivity and sensitivity of the method. The technique of current-scan polarography has also been applied in the study of electron-transfer [70] and coupled electron-transfer-ion-transfer [71,72] reactions at the ITIES in this configuration. 

Principles and Characteristics A substantial percentage of chemical analyses are based on electrochemistry, although this is less evident for polymer/additive analysis. In its application to analytical chemistry, electrochemistry involves the measurement of some electrical property in relation to the concentration of a particular chemical species. The electrical properties that are most commonly measured are potential or voltage, current, resistance or conductance charge or capacity, or combinations of these. Often, a material conversion is involved and therefore so are separation processes, which take place when electrons participate on the surface of electrodes, such as in polarography. Electrochemical analysis also comprises currentless methods, such as potentiometry, including the use of ion-selective electrodes. 

Fig. 3.42 represents the symmetric bell shape curve of 7, i.e., the genuine fundamental harmonic ac polarogram, which means the curve of only 7F discriminated for 7C, e.g., by means of phase-selective ac polarography. The term "fundamental is related to the character of the polarographic cell as a non-linearized network whose response is not purely sinusoidal but consists of the sum of a series of sinusoidal signals at first harmonic (o>) response, besides that of the second harmonic (2a>), the third harmonic (3a>), etc. 

Bond and O Halloran42 claim for the combination of phase-selective detection and differential pulse ac polarography a "virtually complete rejection of ic, even at high frequencies and low concentrations . 

Dieker et al.67 used a similar method but applied a dropping amalgam electrode (DAE) and followed amperometrically by means of pulse polarography the anodic dissolution wave of mercury in the presence of an excess of ligand by appropriate choices of pH and titrant they achieved selective determinations of metal ions at low concentrations. 

The way in which automation of electroanalysis can be achieved depends very much on the specific requirements of the application. In order to illustrate this we have selected a number of typical examples. However, in doing so, we did not consider normal automation inherent to the nature of the analytical method, e.g., automatic scanning of the voltammetric curve in polarography and other voltammetric techniques, in addition to many additional refinements within these methods such as those treated already in Chapter 3 therefore, the selection of the examples in this chapter cannot be other than arbitrary, where the borderline between the common and the uncommon in the future certainly will shift towards the former. 

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... 

Reinke, J., J.F. Uthe, H.C. Freeman, and J.R. Johnston. 1975. The determination of arsenite and arsenate ions in fish and shellfish by selective extraction and polarography. Environ. Lett. 8 371-380. 

For the rapid determination of Tc in a mixture of uranium fission products. Love and Greendale have used the method of amalgam polarography. It consists in a selective reduction of technetium at a dropping mercury electrode at a potential of —1.55 V vs. SCE in a medium of 1 M sodium citrate and 0.1 M NaOH. Under these conditions, technetium is reduced to an oxidation state which is soluble in mercury. The amalgam is removed from the solution of fission fragments and the amount of Tc determined in nitric acid solution of the amalgam by a y count. For Tc the measurement accuracy is within 1 %, and the decontamination factor from other fission products 10 . 

The most common analytical methods used were gas chromatography, HPLC, AA spectrophotometry, polarography, colorimetry, and potentiometry with ion-selective electrodes. In this study GC/MS and other more expensive instrumentation were avoided. If sorbent tubes could not be used for gaseous substances, then the less desirable miniature bubblers or impingers were considered. Although these devices are inconvenient they were often used because no better alternatives were available. Bags were used in a few cases where the analyte could not be retained on a sorbent because of volatility and a small tendency to sorb. Filters were used for particulates. Combinations of collection devices were used if we felt that both particulates and vapor might be present in the analyte. 

Polarographic methods have been extremely useful for the determination of the urinary excretion of the 1,4-benzodiazepines. An assay that employs selective solvent extraction and acid hydrolysis of diazepam and its major metabolites, iV-desmethyldiazepam and oxazepam, to their respective benzophe-nones has been employed to measure the urinary excretion of diazepam [183]. A pulse polarographic assay has been reported that will measure the urinary excretion of bromazepam following a single 12-mg dose [184]. The assay employs selective extraction of bromazepam and the 2-amino-5-bromobenzoyl-pyridine metabolite from the deconjugated metabolites, 3-hydroxybromazepam and 2-amino-3-hydroxy-5-bromobenzoylpyridine, into separate diethyl ether fractions. The residues of the respective extracts are dissolved in phosphate buffer (pH 5.4) and analyzed by pulse polarography, which yields two distinct... 

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