Direct determination of iron(II), iron(III) and total iron as UV-absorbing complexes by capillary electrophoresis

Capillary electrophoresis (CE) was investigated for the separation of iron(II) and iron(III) after selective complexation of these species by o-phenanthroline and EDTA added in excess to the sample solution. The cationic and anionic natures of the ferrous and ferric complexes, respectively, allow their easy electrophoretic analysis in a single run in the presence of an electro-osmotic flow. It was ascertained that the addition of the mixed complexing solution does not alter the iron(II)/iron(III) ratio of the sample and no significant evolution of this ratio was observed over a period of ten days. Using direct UV absorbance detection, the developed method allows the simultaneous determination of iron(II) and iron(III) in less than 3 min with R.S.D.<1% for migration times and <3.5% for corrected peak areas. Excellent detection linearity was also obtained. When only EDTA is added as complexing agent, CE allows the rapid direct determination of total iron content, which provides a means for checking total iron recovery. Both methods were successfully applied to monitor a wet chemistry process converting iron(II) into iron(III).