Methods and apparatus enable radiosynthesis of radiolabeled compounds using electrochemical trapping and release. The trapping and release of radioactive isotopes all occur inside a microreactor, a vial or similar device, thus eliminating the need for azeotropic drying and several dead-end filling steps, as well as the necessity to move concentrated radioisotopes from one compartment of the chip to another. These and other features allow radioisotope enrichment to be carried out internally within a radiochemical synthesis chip, providing faster and more robust operation, as well as producing very high radiochemical labeling yields.