Determination of “inorganic” arsenic(III) and arsenic(V), “methylarsenic” and “dimethylarsenic” species by selective hydride evolution atomic-absorption spectroscopy

A technique for the determination of “inorganic” arsenic(III) and arsenic(V), “methylarsenic” and “dimethylarsenic” species is described which is based on the trapping of arsines and selective volatilisation into a heated quartz atomiser tube situated in the optical path of an atomic-absorption spectrometer. Improved reproducibility is obtained by the use of a continuous flow reduction stage and detection limits are approximately 0.25 ng (based on twice the standard deviation of 10 blank measurements). For a typical sample volume of 10 ml this corresponds to a detection limit of 0.025 ng ml–1 of arsenic. Interferences were investigated and depression of results was observed in the presence of silver(I), gold(III), chromium(VI), iron(II), iron(III), germanium(IV), molybdenum(VI), antimony(III), antimony(V), tin(II), manganese(VII) and nitrite. Various approaches to overcoming such interferences were investigated, and for general use masking with EDTA is advocated. The choice of extraction procedures for speciation analysis is discussed.