Determination of NTA and EDTA and speciation of their metal complexes in aqueous solution by capillary electrophoresis

Abstract

The interest in the use of chelates for enhancing metal uptake by plants during phytoremediation and their widespread use in plant nutrient research requires that an easy, reproducible method be developed for chelate detection in a variety of systems. This work examined the use of capillary electrophoresis for chelate analysis. Electropherograms for nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) and their metal complexes were obtained by capillary electrophoresis in a phosphate buffer by direct UV detection at 185 nm. The metals used were Ca(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II), and Fe(III). For the majority of metals studied, linear calibration curves were obtained in the concentration range of 10−1000 μM. The direct method of determination at 185 nm was found to give a higher detection sensitivity than direct detection at 254 nm. Limits of detection for the metal chelate complexes were in the range of 2−50 μM. The analysis was fast (<6 min), exhibited low relative standard deviations for retention time (<1%) and peak corrected area (<5%), and required no complex sample pretreatment. The method was used to demonstrate speciation in complex nutrient media.