High-precision zinc isotope measurement of chemically different geostandards by multicollector inductively coupled plasma mass spectrometry.

RATIONALE

Zinc isotopes are becoming increasingly applicable in high-temperature geochemistry, for example in crust-mantle interaction and volatilization-related processes. The published zinc isotope data for some commonly used reference materials, however, show large interlaboratory offsets. In addition, there is still limited data for zinc isotope compositions of many widely used geological reference materials.

METHODS

For precise and accurate zinc isotopic ratio analysis of chemically diverse geostandards, including ultramafic to felsic igneous rocks, carbonatites, sediments and soils, an improved procedure for chemical purification of zinc was introduced in this study. The factors potentially affecting zinc isotopic ratio measurement were assessed. The accuracy and long-term reproducibility were obtained by measurements on both synthetic solutions and well-characterized geostandards.

RESULTS

Purification of geologic samples with different zinc concentrations and matrix compositions yields consistent elution curves with nearly 100% recovery. Acidity and concentration mismatches and the presence of some matrix elements (e.g., Mg, Ti and Cr) have significant impacts on the precision and accuracy of zinc isotopic ratio measurement. The zinc isotope compositions of a suite of reference materials were measured using this method.

CONCLUSIONS

The present study describes methods for the chemical purification of zinc and high-precision and accurate zinc isotopic ratio measurements using multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS). The long-term external reproducibility for δ Zn values is ±0.04‰ (2SD). High-quality zinc isotope data of chemically different geostandards were reported to stimulate future interlaboratory calibrations.