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

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.

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