High performance centrifugal partition chromatographic separation of alkaline earth metal ions with bis-2-ethylhexylphosphinic acid

The mutual separation of Ca(II), Mg(II), Sr(II), and Ba(II) was studied by high performance centrifugal partition chromatography using 0.16 M bis-2-ethylhexylphosphinic acid in heptane as a stationary phase. Two-step elution of the four metal ions loaded was accomplished with aqueous chloroacetic acid mobile phases (pH 6.50 and 5.30). Ethanol (5%) was added to the pH 6.50 mobile phase for the separation of Sr(II) and Ba(II). The chromatographic conditions were 2,136 partition channels, 800 rpm rotational speed, and 1.5 cm(3)/Min flow rate. The elution curve was obtained by monitoring the absorbance of each metal complex post-labeled with a chromogenetic agent.