Quantitative electrochemical analysis

Electrolytic deposition was used as a qualitative analytical technique in the early years of current electricity, but it was not until 1864 that quantitative electrochemical analysis commenced with the development of electrogravimetry by Wolcott Gibbs.76,77 Electrolytic techniques of analysis were greatly refined by Edgar Fahs Smith at the University of Pennsylvania, who introduced the rotating anode and double-cup mercury cathode. Smith s book on electrochemical analysis ran to six editions.78... 

Quantitative electrochemical analysis was not introduced, however, until 1864, when electrogravimetry was developed by Wolcott Gibbs 3) and C. Luckow (. The technique was further studied by a... 

Coulometry is a quantitative electrochemical analysis based on counting the total electrical... 

For quantitative electrochemical analysis, the constant height SECM imaging mode should be preferred to the contact one. Figure 9.28 presents the iontophoretic transport of Fe(CN)/- across a track-etched PET membrane imaged at a 0.65 pm radius SECM-AFM Pt tip held at a constant... 

For the in situ characterization of modified electrodes, the method of choice is electrochemical analysis by cyclic voltammetry, ac voltammetry, chronoamperometry or chronocoulometry, or rotating disk voltametry. Cyclic voltammograms are easy to interpret from a qualitative point of view (Fig, 1). The other methods are less direct but they can yield quantitative data more readily. 

Scanning electrochemical microscopy (SECM the same abbreviation is also used for the device, i.e., the microscope) is often compared (and sometimes confused) with scanning tunneling microscopy (STM), which was pioneered by Binning and Rohrer in the early 1980s [1]. While both techniques make use of a mobile conductive microprobe, their principles and capabilities are totally different. The most widely used SECM probes are micrometer-sized ampero-metric ultramicroelectrodes (UMEs), which were introduced by Wightman and co-workers 1980 [2]. They are suitable for quantitative electrochemical experiments, and the well-developed theory is available for data analysis. Several groups employed small and mobile electrochemical probes to make measurements within the diffusion layer [3], to examine and modify electrode surfaces [4, 5], However, the SECM technique, as we know it, only became possible after the introduction of the feedback concept [6, 7],... 

Minerals, electrochemistry of — Many minerals, esp. the ore minerals (e.g., metal sulfides, oxides, selenides, arsenides) are either metallic conductors or semiconductors. Because of this they are prone to undergo electrochemical reactions at solid solution interfaces, and many industrially important processes, e.g., mineral leaching and flotation involve electrochemical steps [i-ii]. Electrochemical techniques can be also used in quantitative mineral analysis and phase identification [iii]. Generally, the surface of minerals (and also of glasses) when in contact with solutions can be charged due to ion-transfer processes. Thus mineral surfaces also have a specific point of zero charge depending on their sur-... 

The infusions of electrochemistry into the HTSC arena has been beneficial for the latter, and also fruitful for both fields. The role of electrochemistry has undeniably led to development of alternative methods for synthesizing HTSCs and their precursors, to methods of HTSC protection and modification of HTSC surfaces (including micro-and nanostructuring), to the fabrication of new hybrid devices that include the HTSC units, and also to new types of junctions. Highly sensitive, relatively simple, and reliable methods of the electrochemical analysis of both the volume and the surface of HTSC materials make it possible to quantitatively characterize the interaction of multicomponent oxides with the environment. In turn, electrochemical experimental methodologies have been enriched by new techniques for controlling the state of complicated and unusual objects under conditions unfamiliar to classical electrochemistry. 

The quantitation of enzymes and substrates has long been of critical importance in clinical chemistry, since metabolic levels of a variety of species are known to be associated with certain disease states. Enzymatic methods may be used in complex matrices, such as serum or urine, due to the high selectivity of enzymes for their natural substrates. Because of this selectivity, enzymatic assays are also used in chemical and biochemical research. This chapter considers quantitative experimental methods, the biochemical species that is being measured, how the measurement is made, and how experimental data relate to concentration. This chapter assumes familiarity with the principles of spectroscopic (absorbance, fluorescence, chemi-and bioluminescence, nephelometry, and turbidimetry), electrochemical (poten-tiometry and amperometry), calorimetry, and radiochemical methods. For an excellent coverage of these topics, the student is referred to Daniel C. Harris, Quantitative Chemical Analysis (6th ed.). In addition, statistical terms and methods, such as detection limit, signal-to-noise ratio (S/N), sensitivity, relative standard deviation (RSD), and linear regression are assumed familiar Chapter 16 in this volume discusses statistical parameters. 

Quantitative chemical analysis involves many types of ionic equilibria other than those between acids and bases, and the present chapter samples some of them. The formation of metal complexes takes place in homogeneous solution, and strongly resembles acid-base chemistry. In extraction, two different solvents are used, but both solutions are still homogeneous. Problems of solubility and precipitation involve two different physical forms of the compound of interest one dissolved, the other a solid phase. Electrochemical equilibria also involve at least two phases, of which one is an electronic conductor, typically a metal, and the other an ionic conductor such as an aqueous solution. Despite these differences in their physics, we will encounter much analogy in the mathematical description of these equilibria, which is why the present chapter is best read after chapter 4. 

McGraw-Hill, 1997, and even some remnants of my Spreadsheet Workbook for Quantitative Chemical Analysis, McGraw-Hill, 1992. This is partially because I have retained some of the didactic innovations introduced in these earlier texts, such as an emphasis on the progress of a titration rather than on the traditional titration curve, the use of buffer strength rather than buffer value, and the use of the abbreviations h and A in the description of electrochemical equilibria. However, the present text exploits the power of Excel to go far beyond what was possible in those earlier books. 

Gravimetry is a method of quantitative chemical analysis. It qualifies as a macroscopic quantitative method of analysis because it involves relatively important quantities of a substance to be determined compared to more recent methods, such as electrochemical, spectroscopic and chromatographic means. From this standpoint, it should instead be compared to titrimetric methods. However, it has remained a method of choice for the analysis of standard compounds, those compounds with which the more recent instrumental methods of analysis listed above are calibrated. 

Electrochemical analysis Electrical properties of the analyte in solution Qualitative and quantitative for major to trace level components... 

The effect of H2O on NMC in humid atmosphere was investigated by structural, magnetic and electrochemical analysis on LiNii/3Mni/3Coi/302 (NMC) compounds synthesized by the co-precipitation method [81], The consequence is that immersion of NMC to H2O and exposure of NMC to humid atmosphere led to a rapid attack that manifests itself by the dehthiation of the surface layer of the particles. This aging process occurred during the first few minutes, then it is saturated, and the thickness of the surface layer at saturation is 10 nm. The quantitative analysis of the Raman spectrum of NMC samples was reported in ref. [81]. Upon exposure to ambient atmosphere for 1 day, the spectrum of the same sample shows three... 

Marecek and colleagues developed a new electrochemical method for the rapid quantitative analysis of the antibiotic monensin in the fermentation vats used during its production. The standard method for the analysis, which is based on a test for microbiological activity, is both difficult and time-consuming. As part of the study, samples taken at different times from a fermentation production vat were analyzed for the concentration of monensin using both the electrochemical and microbiological procedures. The results, in parts per thousand (ppt), are reported in the following table. 

In potentiometry, the potential of an electrochemical cell under static conditions is used to determine an analyte s concentration. As seen in the preceding section, potentiometry is an important and frequently used quantitative method of analysis. Dynamic electrochemical methods, such as coulometry, voltammetry, and amper-ometry, in which current passes through the electrochemical cell, also are important analytical techniques. In this section we consider coulometric methods of analysis. Voltammetry and amperometry are covered in Section 1 ID. 

Coulometric methods of analysis are based on an exhaustive electrolysis of the analyte. By exhaustive we mean that the analyte is quantitatively oxidized or reduced at the working electrode or reacts quantitatively with a reagent generated at the working electrode. There are two forms of coulometry controlled-potential coulometry, in which a constant potential is applied to the electrochemical cell, and controlled-current coulometry, in which a constant current is passed through the electrochemical cell. 

From this equation we see that increasing k leads to a shorter analysis time. For this reason controlled-potential coulometry is carried out in small-volume electrochemical cells, using electrodes with large surface areas and with high stirring rates. A quantitative electrolysis typically requires approximately 30-60 min, although shorter or longer times are possible. 

In a quantitative flow injection analysis a calibration curve is determined by injecting standard samples containing known concentrations of analyte. The format of the caK-bration curve, such as absorbance versus concentration, is determined by the method of detection. CaKbration curves for standard spectroscopic and electrochemical methods were discussed in Chapters 10 and 11 and are not considered further in this chapter. 

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