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