SYNCHROTRON X-RAY-FLUORESCENCE AND LASER-ABLATION ICP-MS MICROPROBES - USEFUL INSTRUMENTS FOR ANALYSIS OF EXPERIMENTAL RUN-PRODUCTS

The synchrotron X-ray-fluorescence microprobe (SXRFM) and laser-ablati on microprobe with inductively coupled plasma - mass spectrometer (LAM -ICP-MS) have been found to be efficient instruments for the accurate measurement of a large suite of trace elements in natural and syntheti c minerals and glasses. The small beam-sizes of both instruments (10 a nd 34 mu m in diameter for SXRFM and LAM-ICP-MS, respectively) permit in situ analysis of samples whose cross-section is at least 7500 mu m( 2) (i.e., corresponding to a sampling area of 50 x 150 mu m analyzed b y LAM-ICP-MS in rastered grid). This sampling technique applied to LAM -ICP-MS avoids sample damage and minimizes the depth of penetration by the laser using a single hole. Optimization of both instruments was c arried out using two in-house basaltic glass standards. The lower limi ts of detection of the SXRFM for Rb, Sr, Y, Zr, and Nb are approximate ly 5.5 ppm or less, based upon our in-house standards, and the analyse s have an associated precision of +/- 20% relative. The lower limits o f detection of the LAM-ICP-MS are approximately 2 ppm or less; these a nalyses have a precision of +/- 10 to 15% relative. Both instruments w ere used to measure partition coefficients between a Ti-rich calcic am phibole and a Ti-rich basanitic quenched glass produced experimentally . The D values determined by SXRFM for Sr, Y, and Zr are: D-Sr, 0.32 ( +/- 0.04), D-Y 0.25 (+/- 0.04), D-Zr 0.12 (+/- 0.07). Partition coeffi cients determined by LAM-ICP-MS are: D-Rb 0.22 (+/- 0.04), D-Sr 0.38 ( +/- 0.01), D-Y 0.33 (+/- 0.03), D-Zr, 0.12 (+/- 0.01), D-Nb 0.05 (+/- 0.01). The LAM-ICP-MS was also used to measure the D values for Ba, Ta , La, Ce, Nd, Hf, Sm, and Eu, which are: D-Ba 0.28 (+/- 0.01), D-Ta 0. 07 (+/- 0.02), D-La 0.039 (+/- 0.005), D-Ce 0.067 (+/- 0.002), D-Nd 0. 14 (+/- 0.01), D-Hf 0.33 (+/- 0.01), D-Sm 0.19 (+/- 0.08), and D-Eu 0. 35 (+/- 0.02).