Determination of EDTA, NTA, and other amino carboxylic acids and their Co(II) and Co(III) complexes by capillary electrophoresis

EDTA and NTA were widely used in the processing of nuclear materials and in the production of nuclear energy. Their in-plant chemical transformations and post-disposal chemical and biological transformations generated many additional amino carboxylic acid compounds. Toxic and radioactive metals are frequent co-contaminants of these chelating agents. Some of the resulting metal ion-chelating agent complexes, most notably (60)Co(III)EDTA, resist decomposition and adsorb poorly onto subsurface minerals, thereby facilitating migration. This study sought to separate and detect free amino carboxylic acids and their Co(ll) and Co(lll) complexes in a single run without prior pretreatment using capillary electrophoresis (CE). The electrolyte filling the CE capillary contained 25 mM phosphate buffer (pH 7). Equilibrium calculations performed for this electrolyte identified predominant cobalt species and helped explain the CE findings. Co(lll) complexes are thermodynamically (and kinetically) more stable than corresponding Co(ll) complexes and are readily separated and detected. Co(lll) complexes of EDTA, NTA, and IDA were synthesized and analyzed. Two different diastereomers of Co(III)IDA(2) were found and could be separated. Co(ll)-amino carboxylate complexes range from ones that are not thermodynamically stable in the capillary and therefore not detectable to those that are highly stable in the capillary and yield good linearity.