Two new schemes for TcO4-/MoO42- separations from OH- and MoO42- media using polyethylene glycol (PEG)-based aqueous biphasic systems (ABS) have been developed. The two most important salt solutions in current Tc-99m-generator technologies, OH- and MoO42-, also salt out PEG to form ABS. In liquid/liquid PEG-ABS, pertechnetate can be separated from molybdate with separation factors as high as 10,000. Stripping is accomplished by reduction of the TcO4- and back extraction into a salt solution. The strip solution can be the salt of an imaging agent (e.g., Na(4)HEDPA) and thus may, under the appropriate conditions, be injected directly into the human body. (TcO4-)-Tc-99m can also be concentrated from a dilute load solution of (MoO42-)-Mo-99 in NaOH using an aqueous biphasic extraction chromatographic technique (ABEC). A rinse with K2CO3 assures that all (MoO42-)-Mo-99 is removed from the column, and this is confirmed by a rapid drop in Mo-99 activity by the fourth free column volume (fcv) of rinse. The (TcO4-)-Tc-99m is then eluted with water. This chromatographic separation affords 94% of the (TcO4-)-Tc-99m activity in 5 fcv, with the gamma spectrum showing less than 2 x 10(-4) of the original Mo-99 activity.