Electrochemical and chemical processes for hydride generation in flow injection ICP-MS:: determination of arsenic in natural waters

A flow injection system involving hydride generation is proposed for the determination of arsenic in natural waters by inductively coupled plasma mass spectrometry. The manifold was designed to permit a direct comparison between chemical (NaBH4) and electrochemical (EcHG) processes for hydride generation, using sodium tetrahydroborate or a Nafion membrane, respectively. Reactions were carried out in different manifold sites, and separation/transportation of the evolved gaseous species and quantification occurred in the same devices under similar conditions. Interferences by Co(ll), Ni (Ir), Cu(II), Zn(ll) and Pb(II) were evaluated for both systems. When NaBH4 was used, addition of these species decreased the As signal, whereas for electrochemical arsine formation, the interference effects were dependent on the Pt cathode conditions. Interferences due to the above metals were modified when the cathode underwent Pb deposition. About 60 samples were run per hour and the measurement precision for 10 mu g l(-1) As was characterized by an RSD < 3%. A higher sensitivity was verified for NaBH4 (LOD = 0.05 mu g l(-1) As) than EcHG (0.2 mu g l(-1) As). Accuracy was assessed by using standard reference materials and spiked river water samples.