In-situ separation of AsIII & AsV during sampling procedure in natural water
In natural water (groundwater, drinking water and soil pore water) different arsenic compounds like arsenite, arsenate, mono- and dimethylarsinic acids are found depending on conditions like bacterial activity, Eh, and pH. These compounds are characterised by different toxicology, solubility and the adsorption on solid phases.
The following arsenic compounds are found in natural water:
H3AsO3 H3AsO4 (CH3)AsO(OH)2 (CH3)2AsO(OH)
To determine the different species in water samples hydride- generation atomic absorption spectrometry for the routine speciation of the compounds listed above and ICP-MS for total arsenic were used (see also Poster: “Speciation of arsenic compounds in natural water”).
In natural waters a changing ratio between As(III) and As(V) was observed probably caused by bacterial activity as well as by oxidising or reducing components in the sampled water. In some samples arsenate was reduced to arsenite within days, so that the initial ratio of the samples is unknown. Common methods of stabilising water samples (e.g. addition of acids) affected the As(III) / As(V) ratio as well.
To overcome sampling problems, a simple method for a quantitative separation of arsenate and arsenite was developed.