An improved method of Tl purification for high precision measurement of Tl isotopes by MC-ICP-MS

Thallium (Tl) isotopes are valuable geochemical tracers widely applied in planetary evolution, redox history of ancient oceans, pollution source tracing, and crustal recycling. Contemporary Tl isotope analyses generally rely on either the standard-sample bracketing or element-doping approach to correct for mass bias. However, complex matrices and residual Pb can introduce correction artifacts, making efficient Tl purification a prerequisite for obtaining accurate isotope data. In this study, we developed an improved dual-column purification system composed of AG 1-X8 anion-exchange resin (200–400 mesh) and AG 50W-X12 cation-exchange resin (200–400 mesh), enabling highly efficient separation and purification of Tl from natural samples. Isotopic measurements were performed on a Nu Plasma II multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS), using Pb as an internal standard for mass-bias correction. The optimized protocol yields Tl procedural blanks <1 pg and Pb blanks <13 pg. Long-term monitoring of the NIST SRM 997 Tl standard produced ε 205 Tl = 0.0 ± 0.7 (2SD, n = 214). The measured ε 205 Tl values for the ferromanganese nodule reference materials NOD-A-1 and NOD-P-1 are 10.8 ± 0.8 (2SD, n = 8) and 3.6 ± 0.8 (2SD, n = 5), respectively, both in excellent agreement with published data. These findings confirm that the method achieves effective matrix removal and Pb elimination, ensuring analytical accuracy and reliability. The developed purification and analytical protocol offer a solid foundation for future Tl isotope investigations of soil and related terrestrial materials. • Developed a tandem chromatographic procedure achieving ultra-low Tl (<1 pg) and Pb (<13 pg) blanks for Tl isotope analysis. • Long-term reproducibility of ε 205 Tl NIST 997 = 0.0 ± 0.7 (2SD, n = 214). • Accurate e 205 Tl analysis and effective matrix and Pb removal are validated by measuring NOD-A-1 and NOD-P-1.