FRACTIONATION OF CALCIUM ISOTOPES IN CATION-EXCHANGE CHROMATOGRAPHY

Ion-exchange displacement chromatography of calcium has been carried o ut successfully for the purpose of observing calcium isotope fractiona tion effects. Small but definite accumulation of the heavier isotopes has been observed at the front parts of the calcium adsorption bands, which means they are preferentially fractionated into the solution pha se. The average values of the single-stage separation factor minus one per unit mass difference between isotopes (epsilon/DELTAM) have been 2.0 x 10(-5) for the calcium chloride system, 5.2 x 10(-5) for the cal cium lactate system, and 2.3 x 10(-5) for the calcium acetate system a t 25-degrees-C. The reduced partition function ratios of the calcium s pecies involved in the present study have been estimated by using sepa ration factor data and available data on calcium hydration under appro priate assumptions. The reduced partition function ratios of the compl ex species have been found to be larger than that of the simple hydrat ed calcium ion, which is a cause of the experimental results that the separation factor values of the calcium lactate and acetate systems ar e larger than that of the calcium chloride system. It has also been fo und that, for the alkali and alkaline earth metals, the magnitude of i sotope effect per unit mass difference between isotopes accompanying p ure ion exchange is nearly inversely proportional to the square of the atomic mass.