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Vol. 1 No. 1 ABSTRACT A lanthanum (La) co-precipitation method was explored for pre-concentration of oxo-anion forming elements followed by measurement with Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The co-precipitation and subsequent washing and elution steps were performed in a 25 mL-volume syringe in order to save the sample consumption and to avoid the contamination from the experimental environment. In the present work, various parameters such as the concentration of La added into the sample solution, the pH, aging time, and so on were optimized to obtain good recoveries and analytical detection limits for V, As, Se, Sb, and W. Generally, in the co-precipitation method, high concentration of precipitant (in this case, La) causes a serious problem of signal memory effect in ICP-MS measurement. To reduce such memory effect, in the present experiment, high level of La was removed by passing the analyte solution (i.e., lanthanum hydroxide dissolved in 1 M HNO3) through a mini column packed with cation-exchange resins. The method thus obtained was evaluated through the measurement of V, As, Se, Sb and W in seawater reference materials (CASS-4 and NASS-5). The recoveries exceeded 80%, and the observed values were in good agreement with the certified values. Thus, the present method was applied to the determination of trace elements in real seawater sample. Keywords: Lanthanum, pre-concentration

ABSTRACT Twenty-four elements in Lake Baikal water were determined by HR-ICP-MS instrument, where two river water reference materials, JSAC 0302 and JAC 0032, were applied to verification of the accuracy of analysis. The concentrations of the analyte elements covered a range of nine orders of magnitude, from approximately 17 µg mL-1 of Ca to less than 2 - 3 pg mL-1 of Cs. Lake Baikal water samples from various water depths showed similar chemical compositions to one another. The distribution of the elements in Lake Baikal water was compared with that in Lake Biwa water, which is the largest lake in Japan. Despite the general similarity in elemental distribution of the two lakes, U and Li were relatively enriched in Lake Baikal water while Y, Mn, and As were relatively enriched in Lake Biwa. Based on the enrichment factor of elements in lake waters, the relative low Li concentration in Lake Biwa water was suggested to be an anomaly, which might be attributed to the deposition of organic deposit that enriched Li. Keywords : multielement analysis, lake water, HR-ICP-MS