A procedure of detecting copper and silver at low ppb and sub-ppb concentration ranges in mixtures in natural water was developed. Both these metals influence significantly biological life in natural water and are considered to be highly toxic even if present in trace amounts.
Our procedure involves the use of differential pulse anodic stripping voltammetry (DPASV) along with the working electrode of a gold alloy containing 4% bismuth. The procedure has been tested and found appropriate for determination of artificial samples prepared by using distilled water as well as for real samples, like spring-, river- and seawater. In the river and seawater samples, copper and silver present in a sub-ppb range was detected with a standard deviation close to 5% by the use of a standard addition method.
The gold alloy electrode containing small amount of bismuth was found to be stable for several weeks, and having a stable baseline making baseline subtraction possible and thereby improving detectability. The copper and silver DPASV peak in 0.05 M NH4Cl was observed at +275 mV and +800 mV, respectively. Moreover, potential of hydrogen evolution was more negative and time stability was higher of the gold-bismuth alloy electrode than those of the genuine gold electrode.
The results show that this electrode can be used over a long period of time without any maintenance, which is important for online determination of pollutants in soil and groundwater.

Key words: Differential pulse anodic stripping voltammetry, Gold-bismuth electrode, Seawater, Copper, Silver, Alloy.

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