Copper polarographic

Solvent for Electrolytic Reactions. Dimethyl sulfoxide has been widely used as a solvent for polarographic studies and a more negative cathode potential can be used in it than in water. In DMSO, cations can be successfully reduced to metals that react with water. Thus, the following metals have been electrodeposited from their salts in DMSO cerium, actinides, iron, nickel, cobalt, and manganese as amorphous deposits zinc, cadmium, tin, and bismuth as crystalline deposits and chromium, silver, lead, copper, and titanium (96—103). Generally, no metal less noble than zinc can be deposited from DMSO. 

Polarographic maxima. Current-voltage curves obtained with the dropping mercury cathode frequently exhibit pronounced maxima, which are reproducible and which can be usually eliminated by the addition of certain appropriate maximum suppressors . These maxima vary in shape from sharp peaks to rounded humps, which gradually decrease to the normal diffusion-current curve as the applied voltage is increased. A typical example is shown in Fig. 16.3. Curve A is that for copper ions in 0.1 M potassium hydrogencitrate solution, and curve B is the same polarogram in the presence of 0.005 per cent acid fuchsine solution. 

The shift of the half-wave potentials of metal ions by complexation is of value in polarographic analysis to eliminate the interfering effect of one metal upon another, and to promote sufficient separation of the waves of metals in mixtures to make possible their simultaneous determination. Thus, in the analysis of copper-base alloys for nickel, lead, etc., the reduction wave of copper(II) ions in most supporting electrolytes precedes that of the other metals and swamps those of the other metals present by using a cyanide supporting electrolyte, the copper is converted into the difficultly reducible cyanocuprate(I) ion and, in such a medium, nickel, lead, etc., can be determined. 

In the application of the polarographic method of analysis to steel a serious difficulty arises owing to the reduction of iron(III) ions at or near zero potential in many base electrolytes. One method of surmounting the difficulty is to reduce iron(III) to iron(II) with hydrazinium chloride in a hydrochloric acid medium. The current near zero potential is eliminated, but that due to the reduction of iron(II) ions at about - 1.4 volts vs S.C.E. still occurs. Other metals (including copper and lead) which are reduced at potentials less negative than this can then be determined without interference from the iron. Alternatively, the Fe3 + to Fe2+ reduction step may be shifted to more negative potentials by complex ion formation. 

A minimum different from the above can be observed on the polarographic wave of peroxydisulphate at about -1-0.1 Volt in the presence of both copper(II) and arsenic(ril) which does not occur with either constituent alone . The decrease in the current due to peroxydisulphate, 4, is kinetic in nature and caused... 

A typical polarographic recording is shown in Fig. 2.1 curve (a) is the po-larogram obtained for chlorinated seawater analysed immediately after chlorination. Identical traces were observed for non-chlorinated seawater and for chlorinated seawater kept in the dark for periods up to 24 h at temperatures up to 40 °C, which indicates a lack of bromate formation under these conditions (BrC>3 < 10 7 M, less than 0.5% conversion of chlorine). Addition of copper sulfate to give a cupric ion concentration in the seawater of 100 parts per billion did not induce measurable bromate production in the dark. Curve (b) was obtained from a chlorinated (4.9 mg/1) seawater solution that was exposed to full sunlight for 70 min. Curve (c), which is offset by 0.4 pA with respect to curves (a) and (b), shows the presence of 1.0 x 10 5 M sodium bromate in seawater. 

Two polarographic methods have been developed for the determination of cohalt(II) at concentrations ranging from approximately 1 to 80 mM in an aqueous sample. For the first method [15], which is suitable for samples containing large amounts of nickel]11), the cobalt(II) is oxidized to Co(NH3)6 in an ammoniacal medium with the aid of sodium perborate, after which the cobalt(III) species is determined. A second procedure [16] entails the use of lead dioxide in an acetic acid-acetate buffer containing oxalate to convert cobalt(II) to the 0(0204)3 ion, which can be subjected to polarographic reduction. This latter approach is well suited to the determination of cobalt in the presence of copper(II), iron(III), nickel(II), tin(IV), and zinc(II), whereas the chief interferences are cerium, chromium, manganese, and vanadium. 

Conditioning of the manganese oxide suspension with each cation was conducted in a thermostatted cell (25° 0.05°C.) described previously (13). Analyses of residual lithium, potassium, sodium, calcium, and barium were obtained by standard flame photometry techniques on a Beckman DU-2 spectrophotometer with flame attachment. Analyses of copper, nickel, and cobalt were conducted on a Sargent Model XR recording polarograph. Samples for analysis were removed upon equilibration of the system, the solid centrifuged off and analytical concentrations determined from calibration curves. In contrast to Morgan and Stumm (10) who report fairly rapid equilibration, final attainment of equilibrium at constant pH, for example, upon addition of metal ions was often very slow, in some cases of the order of several hours. 

Turner, D.R., Varney, M.S., Whitfield, M., Mantoura, R.F.C. and Riley, J.P (1987) Electrochemical studies of copper and lead complexation by fulvic acid. II. A critical comparison of potentiometric and polarographic measurements. Sci. Total Environ., 60, 17-34. 

Reduction of 3 -iodopropionitrile at the potential of the first polarographic (1 e) wave yields Hg (CH2 CH2 CN)2, Sn2 (CH2 CH2CN)6, Pb(CH2 CH2 CN)4 and T1(CH2CH2CN)2I at Hg, Sn, Pb, or T1 cathodes 481 When ethyl or butyl iodide is reduced at platinum or copper cathodes in DMF dimers R2 and disproportionation products, RH, RH(-H2), are formed 482,483,48S Formation of these are attributed to radicals originating both from tire cathodic cleavage of the R-I and the R2-N(CH3)2 bond 482 The ammonium salt is formed by alkylation of DMF. 

A polarographic study on complexes formed between pilocarpine and various imidazoles and copper was carried out. The half-wave potentials of reduction waves of pilocarpine in a copper citrate medium were recorded and found to be a function of the imidazole concentration at low copper concentrations (83). 

Polarographic behavior of copper(II) and copper(I) species in the presence of various ligands has been investigated (154, 215, 258, 279, 343). In some instances, however, no copper(I) intermediate was observed in the reduction to copper amalgam at the electrode, e.g., at low concentrations of 1,2-diaminoethane (270) or similar diamines (205) this is in keeping with a value of 4 x 10 for the equilibrium constant (33, 291) of the reaction... 

Evidently it is more important to determine the cupric ion concentration than the total copper concentration in natural waters. Polarographic methods have been used to measure the ligand concentration (complexing capacity) (10) and to determine stability constants for some strong chelators (11). 

The copper in Cu(acac)2 was determined polarographically after mineralization by the closed flask combustion method . Composition and stability constants were determined... 

Other elements which were determined very often in miscellaneous biological materials are copper, cadmium and zinc. Their polarographic behaviour is very typical and the determination is without problems. Blood, urine and tissues are the most analyzed biological samples. 

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... 

Sher, A. Veber, M. Marolt-Gomiscek, M. Spectroscopic and polarographic investigations copper(II)-penicillin derivatives. Int. J. Pharm. 1997, 148, 191-199. 

Polarographic studies of formation constants of copper(ii)-salicylate complexes have been reported. An e.p.r. study of CuCl2,DH2 (DH2 = dimethylglyoxime) shows high symmetry spectra indicative of a centre of inversion which connects two molecules of complex in the unit cell. Ten new complexes of copperfn) with NN-disubstituted-2-aminoethanol N-oxide have been synthesized. ... 

Figure 15 DP/DME polarographic curves for copper, tin, lead and cadmium in waste water.

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