Investigations of the mobility of radioactive and nonradioactive substances in the environment are important tasks for the development of a future disposal in deep geological formations. Dissolved organic matter (DOM) can play an important role in the mobilization of metal ions due to complexation. In this study, we investigate the complexation behavior of humic acid (HA) as a model substance for DOM and its influence on the migration of europium as homologue for the actinide americium and uranium as the principal component of nuclear fuel. As speciation technique, capillary electrophoresis (CE) was hyphenated with inductively coupled plasma mass spectrometry (ICP-MS). For the study, 0.5 mg center dot L-1 of the metals and 25 mg center dot L-1 of (purified Aldrich) HA and an aqueous solution sodium-perchlorate with an ionic strength of 10 mM at pH 5 were used. CEICP-MS clearly shows the different speciation of the triple positively charged europium and the double positively charged uranyl cation with HA.