The interaction of copper ions with peptides was investigated by electrospray mass spectrometry. Two electrospray micro-emitters were compared, the first one with a platinum electrode using a copper(II) electrolyte solution containing a peptide sample, and the second one with a sacrificial copper anode in a water/methanol solution containing only a peptide (i.e., angiotensin III, bradykinin, or Leu-enkephalin). The former yielded mainly Cu2 complexes either with histidine residues or with the peptide backbone (Cu complexes can be also formed due to gas-phase reactions), whereas the latter can generate a mixture of both Cu and Cu2 aqueous complexes that yield different complexation patterns. This study shows that electrospray emitters with soluble copper anodes enable the study of Cu(I)–peptide complexes in solution.