Copper coulometric

Selecting a Constant Potential In controlled-potential coulometry, the potential is selected so that the desired oxidation or reduction reaction goes to completion without interference from redox reactions involving other components of the sample matrix. To see how an appropriate potential for the working electrode is selected, let s develop a constant-potential coulometric method for Cu + based on its reduction to copper metal at a Pt cathode working electrode. 

Electroanalytical application of hemispherical [35,36], cylindrical [37,38] and ring microelectrodes [39] has been described. A hemispherical iridium-based mercury ultramicroelectrode was formed by coulometric deposition at -0.2 V vs. SSCE in solution containing 8 x 10 M Hg(II) and 0.1M HCIO4 [35]. The radius of the iridium wire was 6.5 pm. The electrode was used for anodic stripping SWV determination of cadmium, lead and copper in unmodified drinking water, without any added electrolyte, deoxygenation, or forced convection. The effects of finite volume and sphericity of mercury drop elecPode in square-wave voltammetiy have been also studied [36]. 

An advantage of the technique is the use of an electrical standard to replace chemical standards and the problems associated with their preparation and stability. The coulometric titration also permits the generation of reagents such as copper(I) or bromine, which are difficult to employ as standard solution, or others such as silver(II) or chlorine, which are virtually impossible to use in any other way. A disadvantage of the coulometric titration is its lack of specificity. 

In most electrochemical measurements solutions are made up to an arbitrary volume that usually is at least 1 cm3. However a few microcells have been described for work with solution volumes that are well below 1 cm3. The coulometric determination of silver ion in cell volumes as small as 20 /iL (formed by a thin copper sheet and a cavity of beeswax) has been discussed.62... 

Coulometric determinations of metals with a mercury cathode have been described by Lingane. From a tartrate solution, copper, bismuth, lead, and cadmium were successively removed by applying the appropriate cathode potential, which was selected to correspond to a region of diffusion-controlled current determined from current-voltage curves with a dropping mercury electrode. With a silver anode, iodide, bromide, and chloride can be deposited quantitatively as the silver salt. By controlling the anode potential, Lingane and Small determined iodide in the presence of bromide or chloride. The separation of bromide and chloride, however, was not successful because solid solutions were formed (Section 9-4). 

It has been reported that this dicopper complex undergoes an irreversible copper-centered reduction at — l.OV in DMSO and two oxidation steps at p = -t-0.20 V and E° = -t-0.62 V, respectively. The less anodic process, which is not fully reversible and possesses a return peak at p = -0.1 V, is difficult to assign, whereas the more anodic process, which is chemically reversible, has been assigned to electron removal processes from the ferrocenyl fragments [191]. Unfortunately, controlled potential coulometric tests have not been performed to determine the number of electrons involved in each electron-transfer step. We should like to think... 

The simplest methods of HTSC analysis are based on the determination of the products of sample dissolution in acidic media. Potentiometric, amperometric, or coulometric titrations are frequently used (mainly for YBCO ceramics [525-527] and their analogs with other rare-earth elements [528, 529], and also for BSCCO [530]). We note particularly the method of potentiostatic coulometric analysis [531], which allows one to analyze thallium cuprate samples over a wide range of the Tl/Cu ratio, and also the method of flow-through coulometry for determining the effective valence of copper [532]. The polarographic determination of Cu content in the samples obtained by dissolving HTSCs in concentrated alkaline solutions with special... 

Although coulometric principles for analytical work were discussed by Szebeledy and Somogyi [101] in 1938, Hickhng [102] wrote of determining copper by controlled potential coulometry in 1942. The current in direct coulometry decreases exponentially with time. The time to reach a quantitative completion, for most analytical apphcations, can be taken as that time when the current has decreased to a value indicative of analyte concentration in solution of 10- M or less. The final concentration will depend upon the requirement for analytical completion for the reaction involved. Alternatively, the critical time can be determined when some indicator system shows the required analyte or reactant concentration has been reached. 

Recently a convenient and precise method has been devised for the determination of thermodynamic data for copper (I)-olefin complexes 67> based on the coulometric generation of Cu(I) and potentiometric measurement of the Cu(I) activity in a lithium perchlorate-2-propanol medium. The formation constants for the reaction Cu(I) (2-propanol) + olefin (2-propanol) Cu(I) olefin (2-propanol), were found to be linearly related to those of the corresponding... 

In fact, one of the earliest electroanalytical (coulometric) methods was the determination of the thickness of tin coatings on copper wires (80). 

The second type of cell is a mercury pool type. A mercury cathode is particularly useful for separating easily reduced elements as a preliminary step in an analysis. l or example, copper, nickel, cobalt, silver, and cadmium are readily separated from ions such as aluminum, titanium, the alkali metals, and phosphates. The precipitated elements dissolve in the mercury little hydrogen evolution occurs even at high applied potentials because of large overvoltage effects. A coulomet-ric cell such as that shown in Figure 24-5b is also useful for coulometric determination of metal ions and certain types of organic compounds as well. 

A constant-potential coulometric determination of copper is being done using a mercury-pool cathode and a water coulometer. A volume of 32.14 ml of hydrogen-oxygen mixture is obtained. The temperature of the gas is 24.0°C and the barometric pressure in the room is 752.0 mm of mercury. The water vapor pressure above the 0.1 M sodium sulfate solution in the coulometer is as follows ... 

The cyclic voltammogram of Cu UPD on Au(lll) shows two well-defined pairs of current peaks A1/A2 and BxjBi corresponding to energetically different adsorption/desorption processes (Fig. 15) [320-322, 337]. In the first step (peak Ai), the transition between randomly adsorbed copper and (hydrogen) sulfate ions into an ordered layer of copper atoms (electrosorption valency y 1.8 [339, 340]) and coadsorbed sulfate ions takes place. The resulting ( 3 X 3)R30° structure was first observed by ex situ LEED and RHEED experiments [354], and later confirmed by in situ SXS [350], STM [341-343], and AFM [344]. QCM [352, 353], chrono-coulometric [339, 340], and FTIR-... 

The OTTLE method is very useful for slow electron transfer kinetics such as those of biological redox processes, in which a mediator is frequently used in an indirect coulometric titration [6, 36] and metal complexes with slow heterogeneous kinetics. An example of the latter is a copper complex in which the Cu(II/I) couple very often shows a broad quasi-reversible wave due to slow heterogeneous kinetics. In this case, spectroelectrochemistry is a useful method for obtaining accurate E° values [37]. 

The coulometry methods based on the physical law which sets the link between the weights of turned electricity and quantity of spent electricity. In many cases the electro generated coulometrical titrate enters in the oxidation process with organic substratum on the mechanism of reaction with the electron carriers. The most effective carriers ate the variable valence metals ions and its components oxidants—chrome (VI), manganese (III), cobalt (III), cerium (IV), vanadium (V), copper (II) deoxidants—cobalt (II), chrome (II), vanadium (HI), titanium (III), iron (II), copper (I), tin (II). The wide area of practical use of the halide ions (chloride-, bromide-, iodide-ions) highlights them apart Ifom a number of reagents—electron carriers. Halide—ions are... 

In both groups of tests described here, standard metal coupons should be included in each test to ensure that the test chamber is giving reproducible results. Copper coupons are a good standard because copper is commonly used in electronic devices, it is sensitive to most corrodents, and its oxide thickness is easily measured by coulometric reduction. 

Figure 10.183 Reversed-phase separation of the accelerator and leveler in a used acid copper bath with coulometric detection. Separator column Thermo Scientific Accucore Cl 8, 2.6 (im column dimensions 150 mm x 4.6 mm i.d. column temperature 40 °C eluent (A) water, 2.5 g sodium perchlorate, 2.5 mt of 10% perchloric acid, (B) MeOH, and (C) MeCN/ MeOH (80 20 v/v) with perchlorates as above ...

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