A new procedure for separating thallium from geological materials prior to stable isotope ratio determination by MC–ICP–MS

In this paper, a simple and efficient method is presented for the separation of Tl from various complex geological samples and subsequent accurate and precise Tl isotope measurements by multi-collector inductively coupled plasma–mass spectrometry (MC–ICP–MS). Chemical separation involves a two-stage tandem column method with tributyl phosphate (TBP) extraction resin and AG50W-X12 cation ion-exchange resin, which efficiently separate Tl from the matrix, interfering elements, and sulfate ions. External normalization to NIST SRM 981 Pb and standard–sample bracketing using NIST SRM 997 Tl were utilized for the instrumental mass bias correction. The ε205TlNIST 997 data are reported as the per 104 deviation of 205Tl/203Tl from NIST SRM997 (Rehkämper and Halliday, 1999; Vaněk et al., 2016). The overall external precision for the ε205TlSRM 997 values is estimated to be ±0.6 (2SD; n > 1000) and ± 0.8 (2SD; n = 5) based on repeated analyses of NIST SRM 997 and the geological reference material NOD-A-1, respectively. The Tl isotopic compositions of nine well-documented geological reference materials are in good agreement with the values reported in previous studies, confirming the validity of our new analytical procedure for the accurate determination of Tl stable isotopic compositions of geological samples.