Determination of chelating agents and metal chelates by capillary zone electrophoresis

Abstract

Abstract. Aminopolycarboxylic acids such as diethylenetriaminepentaacetic acid (DTPA) are commonly used as chelating agents in many pulp and paper industries, particularly as scavengers of metal ions which catalyze the decomposition of hydrogen peroxide used as a bleaching agent. Concern for the effect of waste DTPA in the aquatic environment has led to a need for the development of methods to determine its levels in waste water. This paper describes the determination of free DTPA and several metal-DTPA complexes in water and waste water by capillary zone electrophoresis. The optimization of separation conditions included the selection of an appropriate carrier electrolyte composition (pH, organic solvents, ion-pairing reagents) and the systematic investigations of selective complexation of free DTPA as well as metal exchange reactions for metal-DTPA complexes in order to achieve selective and sensitive direct UV detection. The determination of DTPA in waste water from a paper mill was possible in the low ppm range.Key words" aminopolycarboxylic acids, metal chelates, capillary zone electrophoresis, waste water.Chelating agents such as aminopolycarboxylic acids are widely used as metalmasking additives in various industrial branches, for instance in the pharmaceutical industry, the food industry and in the paper industry. Pulp and paper industries using hydrogen peroxide bleaching of the pulp require chelating agents to remove metal ions which would lead to a decomposition of the bleach chemical and cause excessive usage of hydrogen peroxide. Diethylenetriaminepentaacetic acid (DTPA) is the preferred chelating agent in the paper industry. Like other aminopolycarboxylic acids, its release to the environment may affect the distribution of metals within aquatic ecosystems and may remobilize heavy metals from sediments. Therefore, the concern for the effect of waste DTPA has led to a need for the development of methods to determine the levels of free DTPA and its complexes with iron, copper, zinc and manganese in waste water.Mixtures of various aminopolycarboxylic acids are best determined by gas chromatography after derivatization of the carboxylic group by esterification [-1-3].

Environmental fate and microbial degradation of aminopolycarboxylic acids

“…Attempts to exploit capillary electrophoresis have been made to assess the speciation of APCAs, in particular of EDTA and DTPA. But this method is restricted to rather stable complexes and its sensitivity is still too low for detecting complexes in environmental samples [72,73]. Nonetheless, making use of the photolability of Fe(III)EDTA and the slow exchange kinetics of NiEDTA with Fe(III) ions, analytical methods were developed to distinguish Fe(III)-EDTA and NiEDTA from other EDTA complexes even when present at low, environmentally relevant concentrations [7,64].…”

Rapid Separation and Quantification of Iron in Uranium Nuclear Matrix by Capillary Zone Electrophoresis (CZE)

“…In the present case, since both uranyl and ferric ions (in their hydrated form) have little difference in their charge densities, it is difficult to separate them under normal conditions and addition of a complexing agent is essential for their separation. The organic ligands reported in literature for complexing Fe(III) in CE studies [30][31][32][33][34][35][36]39] may not be suitable in the present case due to the reasons already mentioned above. Hence, it was proposed to consider chloride as ligand as well as carrier electrolyte since its complexation ability with UO 2 2+ and Fe 3+ ions is different and they tend to form cationic complexes of different charges.…”

“…CZE separation of Fe(II) and Fe(III) was demonstrated after complexing with o-phenanthroline and EDTA respectively and the same indicates separation feasibility of Fe(III) as its EDTA complex [35]. Another study reports the separation of Fe(III) as its DTPA complex [36]. In these reported methods, for the determination of either total iron or speciation, Fe-aminocarboxylic acid anionic complex was separated from other metal-aminocarboxylic acid anionic complexes.…”

A Potentiometric Detection Technique for Chelating Agents after Separation by Capillary Zone Electrophoresis

“…Unfortunately, a differentiation between free and complexed analytes is dif®cult. Recently, we have demonstrated the bene®ts of CZE with UV detection for separation of 1 and some of its metal complexes [9]. The use of a selective potentiometric detector in combination with a UV detector adds another dimension of selectivity to the analytical system and should permit an improved detectability of these species.…”