SIMULTANEOUS DETERMINATION OF CR(III), FE(III), CU(II) AND PB(II) AS UV-ABSORBING EDTA COMPLEXES BY CAPILLARY ZONE ELECTROPHORESIS

Capillary zone electrophoresis (CZE) with on-column UV detection was u sed to separate and determine Cr(III), Fe(III), Cu(II) and Pb(II) comp lexes with EDTA. Distribution species-pH diagrams showed that, under t he experimental conditions chosen (pH 5.5), [Me-EDTA](-) and [Me-EDTA] (2-) species for trivalent and divalent metals, respectively, were pre sent. By adding a cationic surfactant, such as TTAB (tetradecyltrimeth ylammonium bromide), to the background electrolyte, an improvement in the peak shapes and shorter migration times were achieved. The chelati ng complexes showed the following order of mobility in electropherogra ms: [EDTA](2-) > [Cu-EDTA](2-) > [Pb-EDTA](2-) > [Cr-EDTA](-) > [Fe-ED TA](-). At 225 nm under a negative applied voltage of 30 kV, using a c apillary of 30.5 cm effective length, in 0.1 M acetate buffer and 0.1 mM TTAB as carrier solution, the complexes were determined within 6 mi n, but the resolution of the Cu(II) and Pb(II) chelates was poor. Howe ver, by using a capillary of 60 cm effective length, simultaneous sepa ration of these chelates the EDTA was achieved. Factorial design was u sed to investigate the effects of chromium, excess of EDTA and boiling time of the solution on the formation of the [Cr-EDTA](-) complex. A fitting model was found in which the EDTA concentration was a signific ant factor. The detection limits of all chelates were in the range 6-2 7 mu M.