Abstract
This study performed a series of comparable experiments (with or without column chromatography) to evaluate whether non-deviated Cu isotope ratios can be obtained directly by Nu Plasma II multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) using standard-sample bracketing with Ga as internal mass bias correction model (C-SSBIN) without column chromatography. Twelve Cu-dominated minerals (copper plate, native copper, chalcopyrite, bornite, chalcocite, digenite, covellite, tetrahedrite, azurite, malachite, atacamite, and cyanotrichite) displayed little drift in δ65Cu values compared with those of minerals with column chromatography, with Δδ65Cuwithout−with ranging from −0.04 to +0.02‰. This means that Cu isotope ratios in Cu-dominated minerals can be achieved without column chromatography, due to the simple matrix and the stability of the machine by using C-SSBIN mode. The acidity and internal standard concentration mismatch effects, as well as the matrix effect, were strictly assessed by Nu Plasma II MC-ICP-MS in a wet-plasma mode in the State Key Laboratory of Continental Dynamics (SKLCD). Finally, a long-term reproducibility of better than ±0.03‰ [n = 38, 2 standard deviations (2s)] were achieved by repeatedly measuring chalcopyrite without column chromatography over 4 months.
Highlights
Copper (Cu) is a transition metal element and has two stable isotopes, 63Cu and 65Cu with relative abundances of 69.17 and 30.83% in nature, respectively (Walker et al, 1958; Shields et al, 1965)
All pairs show similar Cu isotopic ratios with δ65Cuwithout−with spanning from −0.04 to +0.02‰ with CSSBIN with Ga internal standard
The mean δ65Cu values for NWU-Cu-A and tc17-25 during different analytical sessions using direct the standard-sample bracketing (SSB) method were 0.91 ± 0.08‰ (2s, n = 50) and −0.08 ± 0.07‰ (2s, n = 38), respectively. These results indicate that both mass bias correction methods could generate accurate Cu isotopic ratios, but the precision was improved by two times by using the combined standard-sample bracketing with internal standard (C-SSBIN) with Ga as an internal standard
Summary
Copper (Cu) is a transition metal element and has two stable isotopes, 63Cu and 65Cu with relative abundances of 69.17 and 30.83% in nature, respectively (Walker et al, 1958; Shields et al, 1965). To precisely and accurately determine the Cu isotope ratios, there are two steps for natural samples: column chromatography and mass spectrometry. For copper isotope ratios determination, the most commonly used models to improve the analysis accuracy and precision include the straightforward standard-sample bracketing (SSB), combined standard-sample bracketing with internal standard (C-SSBIN) and regression mass bias correction (Maréchal et al, 1999; Zhu et al, 2000, 2002; Archer and Vance, 2004; Yang, 2009; Larner et al, 2011; Hou et al, 2016; Yang et al, 2018). The non-deviated Cu isotope ratios can be acquired on Cu-dominated minerals without column chromatography
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