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.