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A method for the analysis of sub parts per trillion levels of rare-earth elements (REEs) and yttrium (Y) In seawater after preconcentration with solvent extraction and back-extraction has been developed. Almost perfect extraction and backextraction of all REE and Y were achieved by single extraction, and most of the matrix elements were removed during the extraction procedure. Even after 200-fold preconcentration, matrix problems by ICP-MS measurement were negligible. Contamination from reagents and water used during the pretreatment was below 1 % of the concentration of REE and Y In seawater. The standard deviation obtained for triplicate separation of 100and 1000-mL samples of the same seawater was better than 5% for all REE. The average precision of the measurement for all REE and Y after preconcentration of 1000 mL of raw seawater to 5 mL of final measurement solution was calculated to be less than 2.5 %. Since there Is no standard seawater sample for REE and Y, in order to evaluate this novel technique, the analytical results obtained by this method were compared with those obtained by Isotope dilution mass spectrometry coupled with Fe coprecipitation. The comparison indicated the good accuracy of the present method. Sample preparation and measurement could be carried out within 30 min for every sample. Two internal standard elements, In and Cd were used to check sample loss during the extraction and back-extraction procedures and to control the possible matrix effect and Instrument fluctuation.

Some leucogranites from China have been found to display the tetrad effect (Masuda et al., 1987). Abundances of all rare earth elements (REE) in leucogranites from Hunan Province, China, were studied for the first time by inductively coupled plasma mass spectrometry (ICP-MS) in order to in vestigate the shape of the tetrad effect. The chondrite normalized REE pattern consisting of all members except Eu revealed a clear M-type tetrad effect, according to the classification by Masuda et al. (1987). Eu shows a strong negative anomaly. These features may reflect a long history of contact with water. Mathematical analyses of the REE patterns suggest also an octad effect behind the patterns and sym metry between the first (La-Ce-Pr-Nd) and fourth tetrads (Er-Tm-Yb-Lu).

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