Sammendrag
The importance of monitoring the content of heavy metals in waters and effluents is obvious and several analytical methods are available. The methods applied most frequently include Electrothermal Atomic Absorption Spectroscopy and Inductively Coupled Plasma Mass Spectrometry. Being in situ methods, voltammetric and potentiometric stripping methods are also very attractive, but the toxicity of mercury makes limitations in particular for use in the field. We have introduced a non-toxic electrode material similar to dental amalgam for use in voltammetry. Its electrochemical properties are similar to a silver electrode, but possess high hydrogen overvoltage, which enables detection of metals like zinc, nickel and cobalt. Re-cently we have also reported that other silver alloys with a few percent of mercury, lead, bismuth etc. also can be used as electrode material. Such solid electrodes are found to give stable results, thus being useful for online and remote monitoring of waters, effluents and food and beverages. Possible matrix effects can be eliminated by using the method of �medium exchange�. Continuous monitoring of the content of iron in the water is of great interest and for that reason we want to expand the above method, using the same electrode system. From the solubility product of Fe(OH)3 of 4·10-38 , the concentration should not exceed 2.2 ppt even for pH-values of 5.0. However, due to complexation far higher values, frequently above 5 ppm, are common in waters. The ratio of the presence of Fe(II) and Fe(III) can be estimated from potentiometric meas-urements of the redox level of the waters. Thus the iron monitoring can be included in an automatic system. In this presentation, different methods for detecting iron by differential pulse voltammetry (anodic and/or cathodic) with use of the dental amalgam electrode have been evaluated. The influence of high content iron in the detection of other heavy metals like zinc, lead and cadmium will also be reported. Further, a procedure for continuous on-line monitoring of iron in river waters is proposed.
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