Abstract Copper (II) ions appear to be involved in the Alzheimer's disease and seem to influence the aggregation of the amyloid-β1-42 (Aβ1-42) peptide. However, data are not conclusive and still not subject to consensus, copper (II) being suspected to either promote or inhibit aggregation. To address this question, CE-ICP-MS (capillary electrophoresis-inductively coupled plasma-mass spectrometry) hyphenation was proposed as a complementary tool to follow the distribution of copper in the different oligomeric forms, at different substoichiometries and different incubation times. Results clearly indicated the formation of several negatively charged copper complexes and showed the enhancement of the aggregation rate with copper concentration. Moreover, the variations of copper (II) speciation suggest different aggregation pathway, even for substoichiometric ratios.