A new, rapid sample preparation method to improve the assay of uranium and plutonium by mass spectrometry has been developed at the Westinghouse Savannah River Site (SRS). The method is applied to the analysis of mixed plutonium-uranium oxide materials but can be applied to low-level mass spectrometry analyses as well. The new method uses a single extraction chromatographic column to separate and purify both uranium and plutonium for isotopic assay by thermal ionization mass spectrometry. A dual uranium/plutonium spike isotope dilution technique is used to allow rapid analysis of uranium/plutonium content and isotopics. A single UTEVA Resin column is utilized to simultaneously separate both uranium and plutonium from the sample matrix. The plutonium and uranium can rapidly removed from the column separately or eluted together for analysis. This new method combines sample preparation into a single, effective separation step that significantly reduces sample preparation time and costs.