A method produces a radioactively marked carboxylate, at least one precursor molecule of the carboxylate being prepared in a solvent including a conductive salt. Radioactively marked carbon dioxide is fed into the solvent. The precursor molecule is electrochemically reacted with the radioactively marked carbon dioxide to form the radioactively marked carboxylate. The radioactively marked carbon dioxide is completely dissolved in the solvent when the precursor molecule is reacted. The radioactively marked carbon dioxide is used for electrochemically synthesizing a radioactively marked carboxylate, the carbon dioxide being completely dissolved in a solvent during synthesis. A microstructure is used for electrochemically synthesizing the radioactively marked carboxylate, radioactively marked carbon dioxide being reacted.