Inorganic arsenic speciation in water and seawater by anodic stripping voltammetry with a gold microelectrode

The determination of arsenic in sea and freshwater by anodic stripping voltammetry (ASV) was revisited because of problems related to unstable peaks and inconveniently strong acidic conditions used by existing methods. Contrary to previous work it was found, that As(III) can be determined by ASV using a gold microwire electrode at any pH including the neutral pH typical for natural waters. As(V) on the other hand, requires acidification to pH 1, but this is still a much milder condition than used previously. This is the basis of a new method for the chemical speciation of arsenic in natural waters. The limits of detection are 0.2 nM As(III) at pH 8 and 0.3 nM combined arsenic (III+V) at pH 1 with a 30 s deposition time. These limits are lowered by extending the deposition time. The detection step at pH 8 was stripping chronopotentiometry (SC) as this was found to give a lower detection limit than ASV. Copper is co-determined simultaneously with arsenic. The method was applied successfully to the determination of arsenic as well as copper in samples from the Irish Sea, mineral water and tap water.