Abstract
Indium and thallium in 35 river water samples and one lake water in Okayama Prefecture, Tottori Prefecture and Shimane Prefecture were determined by inductively coupled plasma mass spectrometry (ICP-MS) . To measure the dissolved indium and thallium, water samples were filtrated with a membrane filter of 0.45 μm pore size and the residues were decomposed with nitric acid and perchloric acid.115In and205Tl were measured, because these isotopes have the highest abundances. Since115Sn interfered the signal of115In, the intensity of115In signal was corrected by measuring the concentration of Sn by ICP-MS. The concentration of In in the filtration residues and dissolved In were in the range of n.m.-18.0 ng/l and n.m.-55.4 ng/l, respectively. Tl in the filtration residues and dissolved Tl were in the range of n.m-1290 ng/l and n.m.-145.2 ng/l, respectively (n.m. means “less than measurement limit”) . Measurement limits (10σ) in the mass measurement for In in the filtration residue and dissolved In were 0.6 ng/l and 0.2 ng/l, respectively, Those for Tl in the filtration residue and dissolved Tl were 7.2 ng/l and 1.3 ng/l respecively. The relative standard deviations of the results (n=3) for In was 9.9-17.7 % and those for Tl was 8.6-14.9 %.
