Accurate and precise determination of Li isotopic compositions by multi-collector sector ICP-MS

Paul B. Tomascak *
Richard W. Carlson
and
Steven B. Shirey

Department of Terrestrial Magnetism, Carnegie Institution of Washington,
5241 Broad Branch Rd. NW, Washington, DC 20015

A new method is presented for the preparation of geological materials (water and rock) and their accurate analysis, by multiple collector magnetic sector ICP-MS, for the isotopic composition of lithium. The based on multiple duplicate and replicate measurements over an eight month period, the precision of this technique is conservatively estimated to be ±1.1permil (2s population), which is similar to the precision of other methods in current use. The d7Li (7Li/6Li relative to the L-SVEC standard) determined for Pacific seawater is +31.8. The d7Li of the basalt standards JB-2 and SRM-688 are +5.1 and +2.8, respectively. The new technique has additional advantages over other methods in small sample size (~ 40 ng Li), rapid analysis (~ 2 samples/hour) and relative insensitivity to trace element contamination of analyte solutions.
keywords: lithium isotopes, magnetic sector, ICP-MS, cation exchange, mass fractionation