Speciation of Co(III), Co(III), and Cu(II) in ethylenediamine solutions by capillary electrophoresis

摘要

A capillary electrophoretic (CE) method for the speciation of Co(II), Co(III), and Cu(II) in electroless copper-plating baths containing ethylenediamine (En) has been developed. The method is based on the selective precapillary derivatization of Co(II) with 1,10-phenanthroline (Phen) followed by CE separation of stable CoPhen_3~(2+), CoEn_3~(3+), and CuEn_2~(2+) chelates. The proposed derivatization procedure protects Co(II) from oxidation by dissolved oxygen and enables rapid determination of all three metal species within a single run. The optimized separations were carried out in a fused silica capillary (57 cm * 75-μm I.D.) filled with an ethylenediamine sulfate electrolyte (20 mmol L~(-1) H_2SO_4, pH 7.0 with En, applied voltage +30 kV) using direct UV detection at 214 nm. The detection limits for a signal-to-noise ratio of 3 and 10 s, hydrodynamic injections were 5 * 10~(-6) mol L~(-1) for Cu(II), 1 * 10~(-6) mol L~(-1) for Co(III), and 4 * 10~(-7) mol L~(-1) for Co(II). Application of the method to the speciation of Co(II), Co(III), and Cu(II) in copper-plating bath samples is also demonstrated.