Fractionation of Strontium Isotopes in Cation-Exchange Chromatography

Strontium isotope fractionation has been observed in cation-exchange chromatography of strontium salts. The heavier isotopes have been found enriched at the front parts of displacement-type chromatograms, which means that the heavier isotopes are preferentially fractionated into the solution phase. The average values of the single-stage separation factor (S) minus one per unit mass difference between isotopes have been 1.0 × 10−6 for the strontium chloride system, 2.9 × 10−6 for the strontium acetate system, and 3.1 × 10−6 for the strontium lactate system at 25°C. No evidence of the odd-even anomalous isotope effects has been observed. The isotopic reduced partition function ratios (RPFRs) of the strontium species involved in the present study have been estimated; the RPFRs of the complex species have been found to be larger than that of the simple hydrated strontium ion, which accounts for the experimental results that the S values of the strontium lactate and strontium acetate systems are larger than that of the strontium chloride system.