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Introducing a Comprehensive Data Reduction and Uncertainty Propagation Algorithm for U‐Th Geochronometry with Extraction Chromatography and Isotope Dilution MC ‐ ICP ‐ MS
Author(s) -
Pourmand Ali,
Tissot François L. H.,
Arienzo Monica,
Sharifi Arash
Publication year - 2014
Publication title -
geostandards and geoanalytical research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.037
H-Index - 73
eISSN - 1751-908X
pISSN - 1639-4488
DOI - 10.1111/j.1751-908x.2013.00266.x
Subject(s) - chemistry , isotope dilution , certified reference materials , thorium , analytical chemistry (journal) , algorithm , analyte , matrix (chemical analysis) , chromatography , uranium , mass spectrometry , mathematics , detection limit , physics , nuclear physics
We present an open‐source algorithm in Mathematica application (Wolfram Research) with a transparent data reduction and Monte Carlo simulation of systematic and random uncertainties for U‐Th geochronometry by multi‐collector ICP ‐ MS . Uranium and thorium were quantitatively separated from matrix elements through a single U/ TEVA extraction chromatography step. A rigorous calibrator‐sample bracketing routine was adopted using CRM ‐112A and IRMM ‐035 standard solutions, doped with an IRMM ‐3636a 233 U/ 236 U ‘double‐spike’ to account for instrumental mass bias and deviations of measured isotope ratios from certified values. The mean of 234 U/ 238 U and 230 Th/ 232 Th in the standard solutions varied within 0.42 and 0.25‰ (permil) of certified ratios, respectively, and were consistent with literature values within uncertainties. Based on multiple dissolutions with lithium metaborate flux fusion, U and Th concentrations in USGS BCR ‐2 CRM were updated to 1739 ± 2 and 5987 ± 50 ng g −1 (95% CI ), respectively. The measurement reproducibility of our analytical technique was evaluated by analysing six aliquots of an in‐house reference material, prepared by homogenising a piece of speleothem (CC3A) from Cathedral Cave, Utah, which returned a mean age of 21483 ± 63 years (95% CI , 2.9‰). Replicate analysis of ten samples from CC3A was consistent with ages previously measured at the University of Minnesota by single‐collector ICP ‐ MS within uncertainties.