Methods and devices for a fully automated synthesis of radioactive compounds for imaging, such as by positron emission tomography (PET), in a fast, efficient and compact manner are disclosed. In particular, the various embodiments of the present invention provide an automated, stand-alone, hands-free operation of the entire radiosynthesis cycle on a microfluidic device with unrestricted gas flow through the reactor, starting with target water and yielding purified PET radiotracer within a period of time shorter than conventional chemistry systems. Accordingly, one aspect of the present invention is related to a microfluidic chip for radiosynthesis of a radiolabeled compound, comprising a reaction chamber, one or more flow channels connected to the reaction chamber, one or more vents connected to said reaction chamber, and one or more integrated valves to effect flow control in and out of said reaction chamber.