The present disclosure relates to the novel multistep procedure for preparation of polymer monoliths for use in solvent exchange, such as methods to exchange and activate fluoride ions on a flow through microfluidic chip for subsequent chemical synthesis. Methods according to the present disclosure include the application of such microfluidic platforms for rapid F18 radiosynthesis on a flow through microfluidic chip with high efficiency, followed by a subsequent nucleophilic fluorination reaction. Various other methods of exchanging and activating fluoride ions on a flow through microfluidic chip are also disclosed. Methods incorporating features of the present invention can be applicable to any flow through microfluidic device in any field, such as radiosyntheses, chemical syntheses, concentration of ions for environmental analyzes and sample preparation such as concentrating minute amounts of analyte to improve the downstream detection.