A new method for the chemical separation and MC-ICPMS measurements of
U-Th-Pa-Ra disequilibria in volcanic samples from a single sample
aliquot is presented. The accuracy and precision of our techniques is
assessed by replicate analyses of the synthetic U and Th isotope
standards IRMM-184 and IRMM-35, and the secular equilibrium rock
standards BCR-2, W-2a and TML A measure of true sample reproducibility
including the errors related to sample processing and the chemical
separation is obtained from analysis of multiple digestions of the rock
standards. U-234/U-238, Th-230/U-238, Pa-231/U-235 and Ra-226/Th-230
activity ratios on ten separate dissolutions of USGS rock standard
BCR-2, for example, reproduce to 0.4%, 1.4%, 1.1% and 2.4% (2 SD),
respectively. All elements (U-Th-Pa-Ra) are separated from a single
spiked sample aliquot and the elemental concentrations are measured on
the same solutions as the isotopic compositions. Analytical artefacts
from determination of elemental and isotopic concentrations on different
sample aliquots due to sample heterogeneity are therefore avoided. In
addition, our new chemical separation protocol is time-efficient and
allows for rapid processing of volcanic samples with less than 25 fg of
Pa and Ra. (C) 2010 Elsevier B.V. All rights reserved.