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Analytical Procedures for the Measurement of Boron Isotope Compositions by Ion Microprobe in Meteorites and Mantle Rocks
Author(s) -
Chaussidon Marc,
Robert François,
Mangin Denis,
Ha Pascal,
Rose Estelle F.
Publication year - 1997
Publication title -
geostandards newsletter
Language(s) - English
Resource type - Journals
eISSN - 1751-908X
pISSN - 0150-5505
DOI - 10.1111/j.1751-908x.1997.tb00527.x
Subject(s) - meteorite , analytical chemistry (journal) , microprobe , fractionation , isotope , chondrite , chemistry , boron , mineralogy , isotope fractionation , isotopes of boron , geology , radiochemistry , environmental chemistry , chromatography , physics , organic chemistry , quantum mechanics , astronomy
An analytical procedure has been developed to measure in situ the 11 B/ 10 B ratio in terrestrial basaltic rocks and meteoritic chondrules having B concentration of less than 1 μg g −1 using a small radius ims3f ion microprobe. The central difficulties for these measurements are (i) the removal of the trace amount of B contamination introduced in the sample during polishing, (ii) the precise calibration of instrumental mass fractionation of B isotopes and (iii) the low count rates of 10 B and 11 B. Contamination experiments conducted with isotopically labelled B enriched in 10 B showed that ultrasonic cleaning in bi‐distilled water (< 1 ng g −1 B) and pre‐sputtering of the analysed area decrease B contamination to the level of 0.01 μg g −1 . Analyses of isotope standards spanning a range of 11 B/ 10 B between 3.93 and 4.20 showed that instrumental mass fractionation was constant within? during one session of analyses. Repeated analyses of a standard glass showed a reproducibility of instrumental mass fractionation between February 1991 and October 1996 of 1.3. Taking into account all sources of error, boron isotope measurements are accurate to within 5 for meteoritic samples having B contents in the range 0.1 to 1 μg g −1 . A slightly better accuracy of 1.5 can be achieved for basaltic glasses which can be sputtered with very intense primary beams.