A novel separation technique for thallium isotope determination via MC-ICP-MS

Thallium isotopes (205Tl and 203Tl) are emerging as a new tool for investigating petrological and geochemical processes related with environmental issue, and specifically in tracing the origin of Tl in polluted sites. Thallium is a contaminant of growing concern from an environmental perspective and human health threats, being listed among the 13 priority pollutants. The available methods for Tl separation prior to MC-ICP-MS analyses requires the use of relatively dangerous reagents and typically not available in common laboratories, such as Br2 and SO2 gases (Rehkämper & Halliday, 1999; Wang et al., 2023). We developed a novel and simple experimental method to overcomes this issue, which resulted also in shortening analytical times with respect to previously adopted procedures. Our experimental method, after conventional acid digestion, needs NaClO addition to the digested samples to ensure a full conversion of Tl into the Tl3+ form. Then the obtained sample solution was loaded in HCl into a tandem column separation, consisting of TBP (tributyl-phosphate) resin (1st column) and Sr-resin (2nd column). The first column makes use of the TBP, which has a strong affinity for Tl3+ (Ghersini, 1975; Bragagni et al., 2023; Wang et al., 2023). After eluting the matrix in HCl, Tl is eluted in HNO3 directly onto the second column. The Sr-resin is only used to ensure that Pb is fully separated from the Tl fraction, thanks to its strong affinity for Pb. Such a procedure resulted in procedural Tl yield of 99±1.3%. Prior to MC-ICP-MS measurements, purified samples were doped with Pb (NIST SRM 981). The instrumental mass discrimination was corrected by internal normalisation to Pb and sample-standard bracketing technique (Rehkämper & Halliday, 1999). Reference materials (AGV-1, BHVO-1, BCR-2, G-2) are used to assess the precision and accuracy of the data.