Copper, reduction

Berlin Institute Method. This method is for determination of invert sugar in products containing not more than 10% invert in the presence of sucrose. It is a copper reduction method that utilizes MbUer s solution, which contains sodium carbonate. 

Knight and Allen. This is a copper reduction method for reducing sugars in white sugar up to 0.02%. It utilizes EDTA to determine excess unreacted copper. Tests undertaken in 1994 to extend the range of this method were unsuccesshil. In spite of poor performance in ring tests, it remains an official ICUMSA method. 

Fig. 3. Evans-diagram for the cementation of Cu2+ and Pb2 with zinc amalgam of different zinc content. If the zinc concentration in the mercury employed for this special extraction technique is low, the anodic zinc-dissolution current density may be diffusion controlled and below the limiting cathodic current density for the copper reduction. The resulting mixed potential will lie near the halfwave potential for the reaction Cu2+ + 2e j Cu°(Hg) and only Cu2 ions are cemented into the mercury.

Another procedure which has adequate sensitivity for determining the glucose in 1 microliter of serum of filtrate, is the method which uses copper reduction, and subsequently determination of the cuprous ion with a suitable reagent (15) However, one must be careful that one has obtained complete precipitation, for, if uric acid or any other impurities remain, false high values will be obtained. This would result in disaster for the hypoglycemic infant. To uncover this condition is often one of the major reasons for doing this test. 

Drugs can also Interfere with laboratory results by negating certain nonspecific oxidation and reduction reactions essential for the chemical assay. Penicillin, streptomycin and ascorbic acid are known to react with cupric Ion thus, false positive results for glucose may occur If a copper reduction method Is used. If the specific enzymatic glucose-oxidase method Is employed, ascorbic acid can cause a false negative result by preventing the oxidation of a specific chromogen In the reaction. 

Spencer and Brewer [144] have reviewed methods for the determination of nitrite in seawater. Workers at WRc, UK [ 145] have described an automated procedure for the determination of oxidised nitrogen and nitrite in estuarine waters. The procedure determines nitrite by reaction with N-1 naphthyl-ethylene diamine hydrochloride under acidic conditions to form an azo dye which is measured spectrophotometrically. The reliability and precision of the procedure were tested and found to be satisfactory for routine analyses, provided that standards are prepared using water of an appropriate salinity. Samples taken at the mouth of an estuary require standards prepared in synthetic seawater, while samples taken at the tidal limit of the estuary require standards prepared using deionised water. At sampling points between these two extremes there will be an error of up to 10% unless the salinity of the standards is adjusted accordingly. In a modification of the method, nitrate is reduced to nitrite in a micro cadmium/copper reduction column and total nitrite estimated. The nitrate content is then obtained by difference. 

Salicylates in moderate to large (anti-inflammatory) doses cause false-negative readings for urine glucose by the glucose oxidase method and false-positive readings by the copper reduction method. 

Wager, H.G. 1954. An improved copper reduction method for the micro-determination of reducing sugars. Analyst 79 34-41. 

As. is the irreversible entropy production during the copper reduction in reactor A and Asg is the irreversible entropy pro-... 

Copper(II). Upon heating the Cu(II) specimen in the vacuum chamber from 100 C to 300°C, ESCA suggests that there is a desorption of surface contaminants and a gradual conversion of Cu(II) to Cu(I) (Figure 9). High resolution ESCA spectra provide additional support for the copper reduction. These spectra will be presented elsewhere. When removed from the vacuum, the heated sample had a reddish brown color, similar to the Q12O standard. 

At the transition between the two current density ranges, the polarization curve for Cu deposition starts diverging from the calculated Tafel curve. This divergence was attributed to the transition from charge transfer to concentration overvoltage control of the copper reduction. It was concluded from these results that the reduction at the cathode surface of metal ions adsorbed on the particles plays a fundamental role in the codeposition mechanism. 

Closed, coppered reduction vessel fitted with stirrer,... 

Fig. 11. Closed, coppered reduction vessel fitted with stirrer, dropping funnel, and reflux condenser, for use with substances volatile with steam.

The reduction of m-nitrobenzenesulfonic acid is carried out by the method given for preparing aniline (page 75), except that the iron need not be etched since the free mineral acid in the press cake is sufficient to start the reaction. In an iron or copper reduction beaker of about 2-liter capacity are placed 250 grams of finely pulverized cast iron and 1 liter of water. This mixture is heated to boiling... 

I.3. Reduced Forms of the Enzyme. The hydrolysis of the product Schiff-base to release product and generate the aminoquinol form of the cofactor may involve water which has been retained in the active site. Dooley and co-workers have provided direct evidence for copper reduction during the interaction of amine oxidases with substrate under anaerobic conditions (Dooley et al., 1991). By varying the temperature at which EPR spectra were recorded, it was shown for amine oxidases from several sources that there is a temperature dependent equilibrium between Cu V aminoquinol TPQ and Cu / TPQ semiquinone. The Cu / TPQ semi-quinone form was found to be stabilised in the presence of cyanide. The... 

Enzyme Kind of type-1 copper reduction and rate ( 610 nm) Kind of type-2 and type-3 copper reduction and rate (—330 nm and/or reappearance of the 6l0>nm band) ... 

Reactions (4.22)-(4.24) are only a subset of all the oxidation reactions possible for copper. Pourbaix considers 22 copper reduction-oxidation reactions in determining the oxidation behavior of copper in pure water. To determine which reactions will domi-... 

One may also speculate that copper reduction reactions other than described by Equation (4.23), are possible and occur simultaneously. In an NH4OH medium, for example, the following reaction ... 

In the absence of copper ions in the slurry or copper metal on the wafer, / , is the only means by which titanium is removed. As copper ions are added to the slurry, either as a by-product of copper polishing or by the addition of a copper salt such as Cu(N03)2, titanium removal also occurs via the galvanic couple with Cu ions, / 2- Increasing the concentration of Cu, increases Ecu2f/cu and moves the copper reduction curve in Figure 4.44b in the noble (positive) direction. Consequently, the corrosion current density for the Cu -Ti exchange reaction increases, increasing R2... 

In order for the copper ion to deposit onto the copper metal, an electron current must flow from the site of the titanium oxidation to the site of copper reduction. This electron transfer process is shown in Figure 4.50. The titanium metal acts as a local anode, while the copper metal acts as a local cathode. We observe this interaction to occur within a distance of approximately 20-40 pm of a copper structure and believe that this distance is limited by the conductivity of the slurry solution. The conductivity of a 1 vol% NH4OH solution is approximately 800 Q cm. 

Urine samples containing beta-lactams shonld be tested for glucose by the glncose oxidase method, since falsely high values are observed with the copper reduction method (366,367). 

A positive result in the black copper reduction test, suggesting alcaptonuria, can follow the use of diatrizoate, iotalamate or iodipamide (320). 

Lee S, Schoen I. Black-copper reduction reaction simulating alkaptonuria. Occurrence after intravenous urography. N Engl J Med 1966 275(5) 266-7. 

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