High stripping voltammetry

The methods of investigation of metal species in natural waters must possess by well dividing ability and high sensitivity and selectivity to determination of several metal forms. The catalytic including chemiluminescent (CL) techniques and anodic stripping voltammetry (ASV) are the most useful to determination of trace metals and their forms. The methods considered ai e characterized by a low detection limits. Moreover, they allow detection of the most toxic form of metals, that is, metal free ions and labile complexes. 

The method of stripping voltammetry (SV) is one of the most perspective methods in concentration range of thallium(I) determination of 10 -10 M. Achievement of high sensitivity of thallium(I) determination needs carrying out its additional concentration and sepai ation from other metals which ai e close by electrochemical properties. For these purposes it is offered to use a method of coprecipitation with collector. The combination of SV and a method of coprecipitation on a collector have shown that minimum detectable concentration can be decreased by 2-3 orders of magnitude. 

Besides trace metals, adsorptive stripping voltammetry has been shown to be highly suitable for measuring organic compounds (including cardiac or anticancer drugs, nucleic acids, vitamins, and pesticides) that exhibit surface-active properties. 

Early work [400] on the application of cyclic and anodic stripping voltammetry to the determination of lead showed a poor correlation between peak current values and Pb11 concentration at high pH values. This is due to the low electrochemical activity of PbOH. 

Most of our understanding of the marine chemistry of trace metals rests on research done since 1970. Prior to this, the accuracy of concentration measurements was limited by lack of instrumental sensitivity and contamination problems. The latter is a consequence of the ubiquitous presence of metal in the hulls of research vessels, paint, hydrowires, sampling bottles, and laboratories. To surmount these problems, ultra-clean sampling and analysis techniques have been developed. New methods such as anodic stripping voltammetry are providing a means by which concentration measurements can be made directly in seawater and pore waters. Most other methods require the laborious isolation of the trace metals from the sample prior to analysis to eliminate interferences caused by the highly concentrated major ions. 

Radiochemical yields are 80-95% for zinc and quantitative for cadmium. The average relative standard deviation was 25% for zinc and better than 10% for cadmium. The detection limit of the method is 50 ppm cadmium in the ash. Analysis of two Illinois coals with unusually high cadmium content (17 and 21 ppm) gave results in good agreement with those obtained by atomic absorption and by anodic stripping voltammetry (4). The recent development and testing of a radiochemical method for the determination of zinc, cadmium, and arsenic in coal and fly ash, by Orvini et al. (14), has already been discussed in the section on arsenic. 

Stripping voltammetry has recently received a great deal of interest due to its high sensitivity and rapid direct assay (see Sec. III.F). Examples using stripping voltammetry for the trace-level determination have included assays for penicillins [121], diltiazem (calcium channel blocker) [122], mitomycin C (quinone-containing antitumor antibiotic) [123], captopril (hypotensive drug)... 

Other metals, such as copper, nickel, or silver, have been used as electrode materials in connection with specific applications, such as the detection of amino acids or carbohydrates in alkaline media (copper and nickel) and cyanide or sulfur compounds (silver). Unlike platinum or gold electrodes, these electrodes offer a stable response for carbohydrates at constant potentials, through the formation of high-valence oxyhydroxide species formed in situ on the surface and believed to act as redox mediators (40,41). Bismuth film electrodes (preplated or in situ plated ones) have been shown to be an attractive alternative to mercury films used for stripping voltammetry of trace metals (42,43). Alloy electrodes (e.g., platinum-ruthenium, nickel-titanium) are also being used for addressing adsorption or corrosion effects of one of their components. The bifunctional catalytic mechanism of alloy electrodes (such as Pt-Ru or Pt-Sn ones) has been particularly useful for fuel cell applications (44). 

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