Mass-independent isotopic fractionation of tin in chemical exchange reaction using a crown ether

Tin isotopes were fractionated by the liquid–liquid extraction technique with a crown ether, dicyclohexano-18-crown-6. The isotopic ratios of mSn/120Sn (m: 116, 117, 118, 119, 122 and 124) were measured by multi-collector inductively coupled plasma spectrometry (MC-ICP-MS) on a Nu Plasma 500 with a precision better than 0.05 permil amu−1 on each isotopic ratio. Odd atomic mass isotopes (117Sn and 119Sn) showed depletions compared to the even atomic mass isotopes (116Sn, 118Sn, 122Sn and 124Sn). We show that this odd–even staggering property originates from the nuclear field shift effect. The contribution of the nuclear field shift effect to the observed isotope enrichment factor was estimated to be ∼35%.