A Common Reference Material for Mass‐Dependent Sn Isotope Compositions: An Inter‐Laboratory Calibration Approach

The lack of a common reference material and notation for Sn isotope measurement has hindered inter‐laboratory data comparison. Six laboratories using various methodologies participated in this inter‐calibration study to identify a suitable reference material and notation for Sn isotope data, enabling reliable cross‐laboratory comparison. We report Sn isotope data for nine USGS geological reference materials (AGV‐1, AGV‐2, BCR‐2, BHVO‐1, BHVO‐2, GSP‐2, SCo‐2, SRG‐1 and W‐2a, with SCo‐2 data reported for the first time), and for single‐element reference solutions (NIST SRM 3161a, SPEX CertiPrep Sn of type CLSN2 and PLSN5, Puri Sn CEZA, Sn Lyon, Sn IPGP). The SPEX CertiPrep Sn types differ in their Sn isotope composition: CLSN2 reference solutions (ICP‐MS standards) are identical to each other, unlike PLSN5 reference solutions (AA and ICP standards). Our Sn isotope data demonstrate that NIST SRM 3161a (lots 070330 and 140917) is isotopically identical across lots and remains stable over time. To facilitate comparison across laboratories using other in‐house reference solutions, we derived conversion factors to NIST SRM 3161a for Puri Sn CEZA (Δ 122/118 Sn Puri Sn CEZA–NIST SRM 3161a = 0.132 ± 0.011‰), Sn Lyon (Δ 122/118 Sn Sn Lyon–NIST SRM 3161a = 0.229 ± 0.016‰) and Sn IPGP (Δ 122/118 Sn Sn IPGP–NIST SRM 3161a = 0.162 ± 0.018‰), demonstrating that the ENS “Sn Lyon” reference solution is not a NIST SRM 3161a reference solution, unlike stated in earlier publications. IPGP data published after 2020 can be converted with our Sn IPGP conversion factor, while earlier IPGP data are more accurate through normalisation to BHVO‐2. For future studies, we recommend using the stable, available and widely used NIST SRM 3161a as the primary Sn isotope reference material and reporting Sn isotope compositions as δ 122/118 Sn NIST SRM 3161a .