Electrochemical method for the determination

Szkiarska-Smialowska, Z. and Janik-Czachor, M., The Analysis of Electrochemical Methods for the Determination of Characteristic Potentials of Pitting Corrosion , Corros. Set., U, 901... 

Wagner pioneered the use of solid electrolytes for thermochemical studies of solids [62], Electrochemical methods for the determination of the Gibbs energy of solids utilize the measurement of the electromotive force set up across an electrolyte in a chemical potential gradient. The electrochemical potential of an electrochemical cell is given by ... 

Takamura et al. have reported an electrochemical method for the determination of chlorpromazine with an anodically pretreated vitreous carbon electrode [164]. Optimal conditions for the pre-treatment were attained by the anodic oxidation of vitreous carbon electrodes in 0.5 mM phosphate buffer (pH 6.7) at 1.6 V V5. S.C.E. for 2 minutes. This was found to enhance the oxidation peak of the cyclic voltammogram for chlorpromazine by a factor of simeq 30. The peak current at +0.75 V was directly proportional to the concentration of chlorpromazine over the range of 0.2-40 pM and the detection limit was 0.1 pM. 

Steady-State Kinetics. There are two electrochemical methods for the determination of the steady-state rate of an electrochemical reaction at the mixed potential. In the rst method (the intercept method) the rate is determined as the current coordinate of the intersection of the high overpotential polarization curves for the partial cathodic and anodic processes, measured from the rest potential. In the second method (the low-overpotential method) the rate is determined from the low-overpotential polarization data for partial cathodic and anodic processes, measured from the mixed potential. The rst method was illustrated in Figures 8.3 and 8.4. The second method is brie y discussed here. Typical current—potential curves in the vicinity of the mixed potential for the electroless copper deposition (average of six trials) are shown in Figure 8.13 (34). The rate of deposition may be calculated from these curves using the Le Roy equation (29,30) ... 

Electrochemical measurements are useful for determining concentrations of electroactive species in solution. Playing the role of solvent, the monomer studied in this chapter is styrene. One of its most remarkable characteristics is the low dielectric constant (e=2.43 at 298.0K) compared with that of water (e=78 at 298.0K). A solvent with a low dielectric constant is a highly resistive medium, in which voltammetric measurements are not evident. Voltammetric measurements in styrene as solvent have not been described before. Papers describing an electrochemical method for the determination of styrene in more polar organic solvents can be found in the literature13-17. 

An interesting electrochemical method for the determination of bound sialic acid has been developed, making use of a potentiometric four-channel thick-film sensor [236]. The sialidase sensor consists of a bilayer of a membrane containing Clostridium perfringens sialidase immobilized in a poly(vinyl acetate)-polyethylene copolymer, which is placed on top of an fT -selective poly(vinyl chloride)-poly(vinyl acetate) indicator membrane. The enzyme-induced release of bound sialic acid leads to a concomitant decrease in pA a of the carboxyl function of sialic acid. This decrease affords a local pH change inside the sialidase-containing sensor membrane, which is monitored by the H -selective indicator membrane. The pH optimum of the sialidase sensor was pH 4 for sialyllactose, mucin and colominic acid. 

An Electrochemical Method for the Determination of the Effective Volume of Charged Polymers in Solution... 

H Greschonig, KJ Irgolic. Electrochemical methods for the determination of total arsenic and arsenic compounds. Appl Organomet Chem 6 565-577, 1992. 

Recently, electrochemical methods for the determination of DNA strand breaks at an electrode have been developed. With these methods, one singlestrand break (ssb) among >2 x 10 intact phospho-diesteric bonds can be determined in submicrogram amounts of DNA. Circular covalently closed super-coiled (sc) DNA is attached to HMDE. If there is a strand break a new electrochemical signal appears (Figure 5A). 

For such equilibration processes it is necessary, on the grounds of electrical neutrality, that both ions and electrons or electron defects must migrate simultaneously whereby the fluxes of ions and electrons are related to one another. The electrochemical method for the determination of chemical diffusion coefficients D wUl be shown here as an example for the mixed conductor wiistite FeO. 

Lucock, M.D., Hartley, R., and Smithells, R.W., 1989. A rapid and specific hplc-electrochemical method for the determination of endogenous 5-methyltetrahydrofolic acid in plasma using solid-phase sample preparation with internal standardization. Biomedical Chromatography. 3 58-63. 

Kadnikova and Kostic have described biocatalytical oxidation of ABTS by hydrogen peroxide using HRP encapsulated in sol-gel glass [47]. Campanella and coworkers have recently presented an electrochemical method for the determination of antioxidant capacity using a biosensor [48]. 

Alonso, A. M., D. A. Guilin, G. Carmelo et al. 2003. Development of an electrochemical method for the determination of antioxidant activity. Application to grape-derived products. Eur. Food Res. Technol. 216 445-448. 

Electrochemical methods for the determination of diffusion coefficients are not as popular as nonelectrochemical methods. Compared to the number of references wi th N M R data, the number of diffusion coefficients determined by electrochemical methods is insignificant... 

Electrochemical methods for the determination of iodide in HCl solution are described in J. Chem. Educ. 75( 1998)775. 

The ionic potentials can be experimentally determined either with the use of galvanic cells containing interfaces of the type in Scheme 7 or electroanalytically, using for instance, polarography, voltammetry, or chronopotentiometry. The values of and Aj f, obtained with the use of electrochemical methods for the water-1,2-dichloroethane, water-dichloromethane, water-acetophenone, water-methyl-isobutyl ketone, o-nitrotol-uene, and chloroform systems, and recently for 2-heptanone and 2-octanone [43] systems, have been published. These data are listed in many papers [1-10,14,37]. The most probable values for a few ions in water-nitrobenzene and water-1,2-dichloroethane systems are presented in Table 1. 

The electrosynthesis of metalloporphyrins which contain a metal-carbon a-bond is reviewed in this paper. The electron transfer mechanisms of a-bonded rhodium, cobalt, germanium, and silicon porphyrin complexes were also determined on the basis of voltammetric measurements and controlled-potential electrooxidation/reduction. The four described electrochemical systems demonstrate the versatility and selectivity of electrochemical methods for the synthesis and characterization of metal-carbon o-bonded metalloporphyrins. The reactions between rhodium and cobalt metalloporphyrins and the commonly used CH2CI2 is also discussed. 

In 1980 Bemhardsson et introduced an automated electrochemical method for CPT determination. The specimen is mounted as described in Section IV.2 (ii) using a stream of argon to avoid crevice corrosion and 0.02-5% sodium chloride as electrolyte. The CPT is determined by a potentiostatic test method using an instrument called the Santron CDT 400 for potential control, temperature control, and current measurements. 

Santagati and associates (2002) reported a method for the determination of amphetamine and one of its metabolites, 4-hydroxynorephedrine by RP-HPLC with precolumn derivatization and amperometric electrochemical detection. The derivatization was performed with 2,5-dihydroxybenzaldehyde as the electroactive reagent. The compounds were separated on a Hypersil ODS RP-18. The detector oxidation was set at +0.6 volts. 

A more reliable method for the determination of the fb potential can be drawn from a thorough investigation of the complete impedance diagram equivalent to the space charge layer. In fact, the main difficulty encountered in the Mott-Schottky plot is the rather wide range potential for the C extrapolation, which necessarily lead to values where electrochemical reactions contribute to changing the surface properties of the substrate. Moreover, the expected linear relationship shows a significant deviation, which is explained... 

In liquid chromatographic analysis of nitrofuran antibacterials, the most popular detector is the ultraviolet visible (UV-vis) spectrophotometer. Nitrofurans exhibit strong absorption at wavelengths around 365 nm and are, therefore, ideal for direct determination (Table 29.5). Detection wavelengths of 275 nm (56, 57) and 400 nm (175) have also been suggested. Electrochemical detection is also frequently applied in liquid chromatographic methods for the determination of various nitrofuran antibacterials in edible animal products (172, 173, 179). 

Cao and Zeng [52] used of an oscillopolarographic method for the determination and the electrochemical behavior of omeprazole. Portions of standard omeprazole solution were treated with 1 ml 1 M ammonia/ ammonium chloride at pH 8.9 and the solution was diluted with water to 10 ml. The diluted solution was subjected to single sweep oscillopolaro-graphy with measurement of the derivative reduction peak at —1.105 V versus saturated calomel electrode. The calibration graph was linear from 0.5 to 10 /iM omeprazole with a detection limit of 0.2 fiM. The method was applied to the analysis of omeprazole in capsules with recoveries of 100-118.6% and RSD of 6.78%. The electrochemical behavior of omeprazole at the mercury electrode was also investigated. 

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