Determination of picogram quantities of rare-earth elements in meteoritic materials by direct-loading thermal ionization mass spectrometry

A procedure for dlrect-loading isotope dliution mass spectrometry (DL-IDMS) of rare-earth elements (REE), alkailneearth metals (Mg, Ca, Sr, and Ba), alkali metals (K and Rb), and Iron In microcomponents of meteorites Is described. Wlthout chemlcal Separation the acld-decomposed sample was directly loaded onto a mass spectrometer fllament and subjected to thermal Ionization mass spectrometry with careful control of the filament current and the oxygen partial pressure. Thls technique permlts, on a routine basis, precise concentration determlnatlons of lndlvldual REE at the levels of >IO-'' g (or mol) In meterorltlc and terrestrlal materials such as chondrules, mlnerai fragments, and basaltic samples. The results demonstrate the presence of hlghly fractlonated REE In microcomponents of meteorites, which indlcates a new chemkal aspect of REE In the early planetary materials. The DL-IDMS technlque can thus be used as the only means of high-preclslon analyses of small planetary materlais with low REE contents.