Tin isotope ratios of eight different geological reference materials were determined using Neptune and Neoma (Thermo Fisher, USA) multi-collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) systems using the ¹¹⁷Sn-¹²²Sn double-spike technique. Tin was purified by two-stage ion-exchange chromatography with a recovery of 85% ± 5%, with isobarically interfering matrix elements being reduced to negligible levels. Doping experiments indicated that the Neoma instrument was less affected by isobaric interferences than the Neptune instrument. The determined δ^124/116Sn_SRM3161a values are consistent with published values, and the long-term (> 6 months) intermediate precision was better than ±0.01‰ amu⁻¹ for both instruments. The method allows the Sn isotope ratios of samples containing ~ 2 ng of Sn to be precisely determined with an Sn solution concentration of 1 ng g⁻¹.