Capillary electrophoresis in metal analysis: Investigations of multi-elemental separation of metal chelates with aminopolycarboxylic acids

Abstract

Capillary zone electrophoresis was applied to the separation of Co(III), Bi(III), Fe(III), Cr(III), V(IV), Pb(II), Hg(II), Co(II), Cu(II) and Ni(II) metal ions complexed with common aminopolycarboxylic acids. Ethylenediaminetetraacetic (EDTA), cyclohexane-1,2-diaminetetraacetic (CDTA) and diethylenetriaminepentaacetic (DTPA) acids were investigated and compared in order to optimize the separation resolution. The influence of carrier electrolyte parameters such as electrolyte nature, pH and concentration upon the electrophoretic behaviour of chelates was investigated and discussed. Two migration modes – counterelectroosmotic and coelectroosmotic – were compared. Better resolution was achieved using counterelectroosmotic conditions (25 kV) with 5 mmol/l DTPA electrolyte at pH 8.5 and direct UV detection at 214 nm. The separation time was less than 8 min, but the resolution of Co(II), Cu(II) and Ni(II) chelates was poor. For all metals studied the calibration graphs were linear over at least two orders of magnitude of concentration. The detection limits were in the range 2·10−6–8·10−6 mol/l. A possibility of simultaneous determination of metal ions with different oxidation states such as V(IV)/V(V) and Cr(III)/Cr(VI) is demonstrated. Examples of electropherograms are presented for different samples. Application of the method to the analysis of metal ions in electroplating bath and waste water samples is also demonstrated.