Copper trace analysis

Feier B, Floner D, Cristea C, Sandulescu R, Geneste F (2013) Development of a novel flow sensor for copper trace analysis by electrochemical reduction of 4-methoxybenzene diazonium salt. Electrochem Commun 31 13-15... 

Analysis of Corexit 9527. Corexit 9527 in natural waters can be analyzed. The method is based on the formation of a Z>w(ethylenediamine) copper(II) complex, extraction of the complex into methylisobutylketone, and atomic absorption spectroscopy [1564]. The method is suitable for a concentration range of 2 to 100 mg/liter, with a precision as low as 5% relative to standard deviation for samples in the middle- to high range. Only a small sample volume (10 ml) is required. The sensitivity may be substantially increased for trace analysis by increasing the sample volume. 

As a result of that reductive process, a deposit of copper metal (denoted in Eq. 2.2 by s for solid ) is formed on the carbon electrode surface. The prominent anodic peak recorded in the reverse scan corresponds to the oxidative dissolution of the deposit of copper metal previously formed. The reason for the very intense anodic peak current is that the copper deposit is dissolved in a very small time range (i.e., potential range) because, in the dissolution of the thin copper layer, practically no diffusion limitations are involved, whereas in the deposition process (i.e., the cathodic peak), the copper ions have to diffuse through the expanding diffusion layer from the solution to the electrode surface. These processes, labeled as stripping processes, are typical of electrochemically deposited metals such as cadmium, copper, lead, mercury, zinc, etc., and are used for trace analysis in solution [84]. Remarkably, the peak profile is rather symmetrical because no solution-like diffusive behavior is observed. 

The availability of instrumentation in the QC laboratory or at the production facility will often influence the choice of the analytical technique. For example, the trace analysis of a DS for three different metal elements (iron, copper, and nickel) can be simultaneously performed by an inductively coupled plasma (ICP). The cost of this instrument, however, is 100,000 or more. For this example, the same analysis can be performed to the level of precision and detection defined in the technical objective by an A A spectrometer. Unlike the ICP, the AA analysis is sequential, and therefore is significantly more time-consuming. The choice of the A A method may be desirable, however, since the instrumentation cost is afraction ofthe cost of an ICP, and often is an instrument already available in a QC or production laboratory. 

Trace analysis including previous element concentration procedures as well as partial matrix removal (II.B.2) produces an increase in RSD with an injection volume of only 10 jal of 7.6 relative percent in a copper concentration of 0.0021 weight percent and to 16 relative percent with a manganese content of 0.00088 weight percent. Use of an automatic injector can improve the reproducibility of the sample volume considerably [14]. 

Anodic stripping voltammetry (ASV) was applied to the determination of copper traces present as Cu(dik)2. The differential pulse technique was used to strip the amalgamated copper from a hanging mercury drop electrode. The experimental variables such as scan rate of electrode potential, deposition potential, deposition time and stirring speed of the solution could be optimized. The linear range of the calibration plot was 0.05-1 (xM and the LOD was 0.014 fiM Cu(II). A method was used for the determination of copper in breast milk and beer as typical examples of application, consisting of minerahzation of the sample, extraction of Cu(II) from the aqueous solution with a 1 M solution of acacH in chloroform and ASV end analysis . 

Results. Phenolic adhesives are usually manufactured with little or no fillers because of their applications. They are soluble in solvents and dilution methods can be readily applied to the analysis of these products but if trace analysis is required for health or environmental reasons destructive methods may be necessary. Excellent results can be obtained for the determination of calcium and copper sulphonate salts added to products using the internal standard method. These low density adhesives can be analysed without resorting to destructive methods (Table 6.22). 

Fig. 8-29. Trace analysis of chloride in an acid copper sulfate plating bath. — Separator column IonPac AS4 eluent 0.0028 mol/L NaHC03 + 0.0022 mol/L Na2C03 flow rate 2 mL/min detection suppressed conductivity injection 10 pL sample (1 1000 diluted).

The largest group of elements comprises those isolated from solution in the elemental form as a result of reduction, usually electrochemical. In acid solution, the electrolytic deposition of metal on a solid cathode is limited to noble and semi-noble metals. Trace analysis of copper and its compounds may serve as an example [100]. An anodic dissolution technique may be applied for the isolation of macroscopic amounts of copper. A sample in the form of a bar, plate, or wire is the anode in the electrolytic system. When current is passed through the electrolyte (nitric acid + persulphate), Cu is deposited on the graphite cathode, while most trace elements accumulate in the solution. In the trace analysis of platinum, the matrix has been also separated on a cathode [101]. 

Only trace amounts of copper are present in biological material, in the general range 0.1-10 /ig/g (0.1-10 ppm). These trace amounts are in complex mixture with innumerable other metals and elements, some of which are present in much larger quantities. In addition the sample size is often limited, as in blood samples from infants and small animals or needle biopsy specimens from tissues. Methods for copper therefore must be highly sensitive as well as highly specific, since the analyst faces the problem of trace analysis on a micro- or ultramicroscale. 

Adsorptive stripping voltammetry (ASV) is another specialised technique where the SMDE electrode is used for reducible species and carbon paste electrodes for oxidisable ones. This allows enrichment (by factors of 100-1000) of ions at the working electrode before stripping them off for measurement this improves the detection limits. This technique is rapid, sensitive (10 "M), economical and simple for trace analysis. The basic instrumentation for stripping analysis is apotentiostat (with voltammetric analyser), electrode and recorder. While voltammetry is generally very useful for compounds that do not have a chromophore or fluorophore, stripping analysis is the best analytical tool for direct, simultaneous determination of metals of environmental concern, e.g. lead, cadmium, zinc and copper in sea water. 

TRACE ANALYSIS OF IRON, NICKEL, COPPER AND VANADIUM IN PETROLEUM PRODUCTS... 

Regarding the sensitivity of commonly used electrodes and sensors towards the individual metals, it depends, of course, upon the electrode used. Nonetheless, a majority of them respond in the order Pb —> Cd —> Zn , when the difference between the first and last one can be substantial with respect to their determination in trace analysis. These three metals can be also simultaneously determined together with copper, where care has to be taken not to have too high concentration of zinc and copper because of formation of their intermetaUics (see below). 

Analysis of Trace or Minor Components. Minor or trace components may have a significant impact on quaHty of fats and oils (94). Metals, for example, can cataly2e the oxidative degradation of unsaturated oils which results in off-flavors, odors, and polymeri2ation. A large number of techniques such as wet chemical analysis, atomic absorption, atomic emission, and polarography are available for analysis of metals. Heavy metals, iron, copper, nickel, and chromium are elements that have received the most attention. Phosphoms may also be detectable and is a measure of phosphoHpids and phosphoms-containing acids or salts. 

Nickel also is deterrnined by a volumetric method employing ethylenediaminetetraacetic acid as a titrant. Inductively coupled plasma (ICP) is preferred to determine very low nickel values (see Trace AND RESIDUE ANALYSIS). The classical gravimetric method employing dimethylglyoxime to precipitate nickel as a red complex is used as a precise analytical technique (122). A colorimetric method employing dimethylglyoxime also is available. The classical method of electro deposition is a commonly employed technique to separate nickel in the presence of other metals, notably copper (qv). It is also used to estabhsh caUbration criteria for the spectrophotometric methods. X-ray diffraction often is used to identify nickel in crystalline form. 

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