A novel and efficient single column separation procedure for high-precision determination of Molybdenum isotope ratio...

Molybdenum (Mo) isotope has been widely used to trace various redox processes in earth science, however, conventional separation methods, typically depend on toxic hydrofluoric acid (HF), redox reagents (e.g., hydrogen peroxide (H₂O₂) and ascorbic acid (HAsc)), or multi-column purification steps, which introduce either safety hazards or operational complexity. In this study, a safe and efficient single-column procedure without use of either HF or redox reagents was developed for Mo separation from various samples for high precision Mo isotope measurements.

This method takes advantage of high selective adsorption of Mo on an in-house TOPO resin and only utilize the diluted HCl - HNO₃ media, achieving an effective matrix removal, a high Mo recovery (>93 %) and low procedural blanks (<0.50 ng). Repeated analyses of NIST SRM 3134, Mo metal, and seawater CASS-6 yielded an external reproducibility better than ±0.06 ‰ (2SD). Mn-doping experiments revealed that Mn/Mo ratios exceeding 0.50 induced significant polyatomic interference, causing measurable negative shifts (>0.10 ‰) in δ^98/95Mo_{NIST SRM 3134} values. The method was validated using 11 geological reference materials, showing good agreement with published values. Additionally, the δ^98/95Mo_{NIST SRM 3134} values of five biological reference materials (e.g., green tea, human hair, pig liver, and fetal bovine serum) were reported for the first time, exhibiting a significant isotopic variation of 1.44 ‰.

Compared with anion/cation-exchange resins or extraction resins, this novel procedure based on in-house TOPO resin depends on dilute HCl - HNO₃ media and effectively purifies Mo from the matrix, with good performance and operational safety. Additionally, the δ^98/95Mo_{NIST SRM 3134} values for biological reference materials provide valuable references for quality assurance and inter-laboratory comparisons in emerging applications of Mo isotopes in biological systems. Overall, this study provided a simpler and safer alternative method for high-precise determination of Mo isotope in various samples.