Anodic stripping voltammetry as an analytical tool Here is how it works and may be applied properly to environmental surveillance, especially where heavy metal contaminants are concerned
Joseph Wang Department of Chemistry New Mexico State University Las Cruces, N.M. 88003
Heavy metals are one class of contaminants that can produce undesirable effects even if they are present in extremely minute quantities. For instance, unlike many other pollutants, they are not biodegradable, and may persist for long time periods. Therefore, techniques are being devised to measure them at very low concentration levels. Anodic stripping voltammetry (ASV) is a sensitive, precise, and economical electroanalytical technique for detecting trace metals. Consequently, ASV has become one of the popular approaches to environmental analysis. Electrochemical methods of analysis are generally applied to the qualitative and quantitative determination of electroactive species in solution. Anodic stripping voltammetry belongs to the voltammetric branch of electroanalytical techniques. Voltammetric techniques are those in which a current response is measured as a function of a potential waveform increasing in amplitude. In ASV, metals are concentrated by reduction into or onto a microelectrode, followed by anodically reoxidizing (stripping) them to produce a peak-shaped plot of
current as a function of potential. Although ASV cannot be regarded as a new analytical technique, new approaches and instruments have been introduced recently that have enhanced the technique’s capabilities. The increasing use of ASV is attributable to its ability to measure simultaneously several elements at concentration levels down to the fractional parts-per-billion (ppb) at a relatively modest cost. (A complete ASV system would cost $4000-5000.) It is fair to say that there is no technique for trace metal analysis that can compete with ASV on the basis of sensitivity per dollar investment. Little expertise is required, and analysis time is on the order of a few minutes. The inherently high degrees of accuracy and precision of ASV stem from its application of Faraday’s law. Comparative studies with other analytical techniques, such as various atomic absorption procedures, have emphasized the particular reliability of ASV in trace metal analysis for all types of environmental matrices, especially in various types of natural
Why anodic stripping voltammetry is successful Sensitivity: detection limits at tl sub parts-per-biiiion level Multi-ion analysis per sample
Precision and accuracy Powerful tool for determining t h e chemical nature of trace mei ions (speciation) Ability to perform on-line mi ysis
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Environ. Sci. Technoi., Voi. 16. No. 2.
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water. The technique has been applied to solving numerous trace metal analysis problems in a variety of other matrices such as food, blood, or fingernail, and has proved to be very sensitive. Moreover, the special property of ASV to be species-sensitive makes this technique an efficient tool in speciation studies of toxic trace metals dissolved in natural waters. Like atomic absorption spectroscopy, ASV is subject to various interferences when it is applied to real life samples; most of these interferences can be eliminated by proper selection of experimental conditions. Water analysis Anodic stripping voltammetry has been used extensively to analyze natural water samples. Ariel and Eisner used ASV, in one of its early (1963) environmental applications, to analyze zinc, cadmium, and copper in Dead Sea brine ( I ) . The major ion content in the Dead Sea water did not interfere with the trace metal determination. Much of the Success in applying ASV for analyzing natural waters is attributed to Florence, who used ASV about 10 years ago to determine trace levels of lead, cadmium, zinc, copper, thallium, bismuth, indium, and antimony in seawater (Pacific Ocean), as well as in fish, seaweed, abalone, and oysters inhabiting the water (2, 3). Since then, and through the 1970s. ASV has been widely used for analyzing about 20 trace metals in different types of natural waters such as oceans, lakes, rivers, as well as in sewage or industrial effluents and tap waters. Waters analyzed came from Lake Superior ( 4 ) , Oslofjord ( 5 ) . the
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0013-936X/82/0916-104A$01.25/0 @ 1982IAmerican Chemical Society
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