The separation of such metal ions as Cu(II), Mn(II), Co(II), Ni(II), Mg(II) and Ca(II) has been investigated by high performance centrifugal partition chromatography (HPCPC) employing di-2-methylnonylphosphoric acid/heptane as a stationary phase. The four transition metal ions have mutually been separated by the two-step elution method, changing the pH of the chloroacetic acid mobile phase, and the two alkaline earth metal ions have been separated by an isocratic elution. The HPCPC system was operated with 2136 partition channels, at a rotation speed of 800 rpm, and at a flow rate of 2.0 cm(3) min(-1). The elution curve was obtained by monitoring the absorbance of each metal complex post-labeled with chromogenic compounds. (C) 2003 Society of Chemical Industry.