An improved calibrated mass spectrometry for absolute copper isotope-ratio measurement using two strategies for mass bias correction factor

Modern advances in multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) have greatly promoted the investigation of copper isotopes in various research fields. To meet the demand, an improved calibrated mass spectrometry for the absolute determination of copper isotopic composition was developed in this study. The method has made progress in the investigation of instrumental mass bias correction factor for copper isotopic analysis using MC-ICPMS through employing two independent strategies. One is the conventional mathematical iterative method based on the MC-ICPMS measurement data; the other one is direct calculation using the absolute copper isotopic compositions in isotopically enriched Cu-63 and Cu-65 materials by developing a TE-TIMS method. The results of K-iter = 0.95563(16)(k = 1) and K-TE = 0.95551(17)(k = 1) were consistent in their standard uncertainties, demonstrated the first cross-validation of these two strategies. Thereafter, the proposed calibrated mass spectrometry were applied to re-measure the copper isotope amount ratios in three isotopic reference materials, resulted in R-NIST SRM 976(65/63) = 0.44547(16)k = 2, R-ERM (R)_AE633(65/63) = 0.44549(16)(k = 2), and R-ERM (R)_ AE647(65/63) = 0.44557(16)(k = 2), respectively. These expended uncertainties were only one third or one fifth of the stated uncertainties in their certificates. Furthermore, the absolute copper isotopic compositions in four natural-abundance samples and a new copper isotopic reference material GBW04624 were determined, given an average atomic weight of copper as Ar(Cu) = 63.5456(4)(k = 2). The delta Cu-65 values of GBW04624 relative to NIST SRM 976, ERM (R)-AE633 and ERM (R)-AE647 were also applied by implementing the C-SSBIN calibration model. This provides an additional independently certified and SI-traceable copper isotopic reference material, in support of various scientific researches.

Automated summary

This study developed an improved calibrated mass spectrometry method for the absolute determination of copper isotopic composition and investigated instrumental mass bias correction factor for copper isotopic analysis using MC-ICPMS through two independent strategies. The results were consistent and validated each other. The proposed method was successfully applied to re-measure copper isotope amount ratios in reference materials, significantly reducing the uncertainties. Additionally, the study determined the absolute copper isotopic compositions in natural-abundance samples and introduced a new SI-traceable copper isotopic reference material.