A method of isolating 186Re according to example embodiments may include vaporizing a source compound containing 185Re and 186Re. The vaporized source compound may be ionized to form negatively-charged molecules containing 185Re and 186Re. The negatively-charged molecules may be separated to isolate the negatively-charged molecules containing 186Re. The isolated negatively-charged molecules containing 186Re may be collected with a positively-charged collector. Accordingly, the isolated 186Re may be used to produce therapeutic and/or diagnostic radiopharmaceuticals having higher specific activity.