Improved Separation of Closely Related Metal Ions by Centrifugal Partition Chromatography

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Abstract
Centrifugal Partition Chromatography (CPC) has been used for the analytical scale separations of adjacent trivalent lanthanides. The stationary phase was 0.1 M Cyanex 272 (bis(2,4,4-trimethylpentyl)phosphinic acid) in heptane and the mobile phase was water at the appropriate pH. Baseline separations of the adjacent lanthanides were achieved with an observed column efficiency of 320 /pm 40 theoretical plates. The column efficiency decreased with flow rate, i.e., the normal Van Deemter behavior was observed. The distribution ratios (D) of selected trivalent lanthanides at different pH values were in general in good agreement with the values determined by batch solvent extraction method. The D obtained with CPC differed markedly from the solvent extraction values inn certain cases resulting in a dependence of separation factor (α) of adjacent lanthanides on pH. This anomaly is under further investigation. The number of theoretical plates, selectivity and resolution of adjacent lanthanides obtained with the current system is ssignificantly better than previously reported. We have demonstrated for the first time, that a mixture of light and heavy lanthanides can been efficiently separated in a single run by CPC, by using gradient pH elution.

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