On-line determination of arsenic species in seawater by selective hydride generation coupled with inductively coupled plasma-mass spectrometry

A method for direct determination of total inorganic arsenic (III+V), arsenic (III) and dimethylarsinate (DMA) in seawater was developed by combining continuous-flow selective hydride generation and inductively coupled plasma mass spectrometry (ICP-MS) is presented. The principle underlying selective hydride generation is based on proper control of the reaction conditions for achieving separation of the respective arsenic species. The effects of pH and composition of reaction media on mutual interference between the arsenic species were investigated in detail. The results indicate that the appropriate media for the selective determination of total inorganic arsenic, DMA and As(III) are 6 M HNO3, acetate buffer at pH = 4.63 and citrate buffer at pH = 6.54, respectively. The concentrations of total inorganic arsenic species, As(III+V), and As(III) were respectively determined and that of As(V) was obtained by the difference between them. As to the concentration of DMA, it was obtained after correction from the interference caused by As(III) and As(V). By following the established procedure, the detection limits (as based on 3-sigma criterion) for As(III+V), As(III) and DMA were 0.050, 0.009, and 0.002 ng/mL, respectively. The reliability of the proposed method was evaluated in terms of precision and spike addition. The results indicated that the precision of better than 3% and spike recovery of 95 to 105% for all the arsenic species tested in the natural seawater samples can be obtained.