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].