Voltammetric Determination of Trace Concentrations of Metals in the Environment

facing the world today is the contamination of the environment by inorganic, organic, and organometallic species. One area of particular interest is the detection of heavy metals and metalloids in environmental matrices and the elucidation of their pathways through various environmental compartments (1–4). Ultimately, these toxic metals are incorporated into drinking water and various food chains. Since metals are biologically nondegradable, they tend to accumulate in various vital organs; therefore, even exposure to trace concentrations of various metal ions can lead to longterm toxic effects. Metal and metalloid ions can be divided into three groups, based on their toxicity (2,4). The metal/metalloids of the first group are toxic at all concentrations and have no known biological functions; this group includes lead, cadmium, and mercury. The ions of the second group (which includes arsenic, bismuth, indium, antimony, and thallium) also have no known biological functions, but are less toxic; however, they are still toxic if present in more than trace concentrations. The final group includes essential metal/metalloids such as copper, zinc, cobalt, selenium, and iron, which are required for various biochemical and physiological processes, and are toxic above certain concentrations. There are a number of requirements for an analytical technique to be useful in environmental analysis (2,4). These include sensitivity, precision, accuracy, dynamic range, ease of pretreatment/sample preparation, ease of automation, cost, suitability for studies in the field, applicability to a wide range of substances, and the capability of determining more than one species. In addition, there is often the added burden that a method be approved by regulatory authorities. Voltammetric determinations are based on the current response of an analyte to an applied potential waveform (the current is plotted as a function of the applied potential, as shown in F1). The magnitude of the peak current is proportional to the concentration of the analyte in solution. Voltammetry exhibits a wide dynamic range, from sub-ppb to ppm or higher. For the higher concentrations (ppm or high ppb), direct measurement by differential pulse voltammetry (DPV) or (Osteryoung) square-wave voltammetry (OSWV) is possible; for lower concentrations, these voltammetric techniques are combined with a preconcentration step (which may be electrochemical or nonelectrochemical). These latter techniques are referred to as stripping techniques (5,6). For many metal/metalloid ions (e.g., lead, cadmium, copper, zinc, antimony, and bismuth), Anodic Stripping Voltammetry (ASV) at a mercury electrode Voltammetric Determination of Trace Concentrations of Metals in the Environment