Determinations of Ga, In and TI in standard rock specimens and chondrites by stable isotope dilution

抄録

The concentrations of Ga, In and T1 in 7 standard rocks and in 11 ordinary chondrites have been determined by stable isotope dilution method employing the thermal ionization mass spectrometer. Prior to the mass spectrometry, these elements were preconcentrated by a cation-exchange column. Reproducibility of the present method is estimated to be less than 1%, as long as the sample is well homogenized. It was found that the sample inhomogeneity is the most important restriction in precise and reproducible determination of the elements even in the standard rock powders carefully prepared. Although two analyses of In and T1 on JB-1 (basalt) and DTS-1 (dunite) show good reproducibilities, quite different values are obtained by repeated analyses of In and T1 in AGV-1 (andesite): 56.4 and 114.4ppb on In, and 0.3966 and 0.963 ppm on T1. Our data of chondrites did not agree so well with earlier measurements. The disagreements are considered to be due to inhomogeneity of elements concerned in the sample. All of three impact-melted LL-chondrites show higher abundances of In and T1 with considerable scattered values, which suggests inhomogeneous distribution of these elements in the meteorites. The isotopic composition of Ga, In and T1 in reagents have been also measured precisely by a thermal ionization mass spectrometer.