Integrated Element Doping and Standard-Sample Bracketing for Enhanced Fe–Zn Isotope Precision in MC-ICPMS

Abstract

Background

Standard-sample bracketing (SSB) and element doping are widely used for correcting instrumental mass bias in Fe–Zn isotope analysis using multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). However, the combined effects of analyte concentration and spike-analyte ratios on measurement accuracy remain underexplored.

Methods

We developed an improved Fe–Zn isotope analysis method that combines SSB with element doping to mitigate concentration effects. By systematically evaluating Ni/Fe and Cu/Zn ratios (0.1–2.1) and analyte concentrations ranging from 0.1 to 2.0 times the concentration of the bracketing standards, we assessed their influence on isotope precision and accuracy.

Results

Our findings indicate that, when low-concentration isotopes are accurately quantified, variations in Ni/Fe and Cu/Zn ratios exert minimal influence on measurement precision. Compared to conventional SSB, the combined approach reduces concentration matching constraints by 30%–50%, broadening the acceptable Fe and Zn concentration ranges. Validation using 10 geological reference materials, including 6 from the United States Geological Survey and 4 from the Geological Survey of Japan, confirmed its reliability, with isotopic values aligning with published data within analytical uncertainty.

Conclusion

The combined approach enhances measurement precision and applicability to diverse geological samples, offering a robust method for Fe–Zn isotope studies.