A single-stage purification method for the precise determination of zirconium isotopic composition in geological samples by double spike MC-ICP-MS

Abstract

Interest in studying zirconium (Zr) stable isotopic fractionation in both low and high-temperature environments has increased significantly in recent years. Multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) is the preferred technique for stable Zr isotope analysis due to its low sample consumption and high precision. However, the multi-column separation steps required to remove interferences and meet the stringent matrix requirements for Zr isotopes during MC-ICP-MS testing typically make the sample preparation process time-consuming. Here, we present a new, simple, and efficient single-pass chromatographic exchange technique for the chemical isolation of Zr from complex sample matrices. This new separation protocol is based on DGA resin and consists of only three elution steps and two types of acid eluents (15 mL 7 mol L⁻¹ HNO₃ and 5 mL 3 mol L⁻¹ HNO₃ + 0.1 mol L⁻¹ HF), which afford straightforward separation of Zr with high yield, good purity, and low blank levels. Zr isotope ratios were measured using Neptune Plus MC-ICP-MS with the ⁹¹Zr–⁹⁶Zr double spike in combination with standard–sample bracketing for mass bias correction. The validity of the proposed method is demonstrated by analyzing eight geological reference materials (including BCR-2, which has an extremely high Mo content of ∼248 μg g⁻¹) with satisfactory results that are in good agreement with published values. Based on repeated analyses of pure standard solutions and geological reference materials, the long-term measurement reproducibility is better than ±0.048‰ for δ⁹⁴Zr. Therefore, the proposed method can be used for the rapid and efficient determination of stable Zr isotope ratios in geological samples.