The ability to detect trace amount of metal ions is important because of the toxicity of heavy metal ions on a broad range of living organisms and the consequence of heavy metals not being biodegradable. To dale, heavy metals in environment are usually measured with spectroscopic techniques, which require samples to be collected and transported to the laboratory for analysis. In situ measurements are highly desirable because they provide an early detection of trace metal contaminants while minimizing errors, labor and cost associated with collection, transport, and storage of samples for subsequent laboratory analysis. One of the promising in situ sensors is based on anodic stripping voltammetry.(l-5) To achieve detection limits of trace elements in the ug/L to ng/L range, a preconcentration or separation technique is normally required, in which metal ions are electrochemically deposited onto a Hg electrode. Following the preconcentration, the electrode potential is scanned to a more positive value to oxidize and strip the deposited metals from the electrode. The oxidation current reaches a peak at a potential characteristic of the metal, which provides the identity of the metal. Other methods include fluorescence-detection,(6-I2) porphyrin derivatives as complexing agent,(7) array-based sensors,(13, 14) magnetic effects,(15) ion-sensitive field effect transistors( 16) and microfabricated cantilevers.(17, 18) While each method has its own advantages and disadvantages, a simple and inexpensive yet reliable and sensitive sensor requires further effort.
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