Liquid mercury is a unique material for the working electrode in voltammetry because of its high negative potential of hydrogen evolution, its ability to form liquid amalgams and the possibility to regenerate continuously a new electrode surface simply by dripping out a new mercury drop from a glass capillary. However, mercury is considered as a toxic heavy metal and, therefore, should be avoided in online apparatuses for use in field.
Because voltammetry is very suitable for field and remote monitoring, issues concerning the use of mercury electrodes in environmental analyses have led to considerable research effort aimed at finding alternative to mercury electrode materials with comparable or better performance.
In this presentation an overview of several compact (non-film) solid amalgam and alloy electrodes will be given, including the dental amalgam electrode [1, 2], silver electrodes alloyed with only a few percent of mercury, silver-bismuth electrode, gold-bismuth electrode, silver-copper electrodes, etc.
The accessible potential windows in different electrolyte solutions for these electrodes will be systematically presented and discussed as well as their possibility for use in detection of several different metals including cobalt, nickel, zinc, cadmium, iron, led, copper, mercury, and silver in low ppb and sub ppb level in real samples will be given. In particular, solid amalgam electrodes are very promising, with acceptable low toxicity, for use in field measurements. Assessment of the toxicity risk and the long-time stability for remote and unattended monitoring will be discussed.
The differences between homogeneous amalgam electrodes, prepared by using techniques known from dental clinical practice, and mercury film or mercury layer electrodes on solid substrates will be reviewed as well. Analogous comparisons will be presented for compact (non-film) alloy electrodes.
Key words: Anodic stripping voltammetry, Solid electrodes, Dental amalgam, Mercury electrode, Heavy metals, Alloy.
1. O. Mikkelsen and K. H. Schroder, Electroanalysis 15 (2003) 679.
2. O. Mikkelsen and K. H. Schroder, Electroanalysis (2003) in press.