Simultaneous determination of 237Np, 232Th and U isotopes in urine samples using extraction chromatography, ICP-MS and gamma-ray spectroscopy

Simultaneous determination of 237Np, 232Th and U isotopes has been demonstrated using extraction chromatographic sample preparation in conjunction with inductively coupled plasma mass spectrometry (ICP-MS). After being spiked with 239Np, 233U, and 230Th tracers, urine samples were wet ashed with HNO3 and loaded onto an extraction chromatographic column. Following elution, samples were spiked with a known quantity of 242Pu and brought to a constant volume. The quantities of 232Th and U in the original sample were then determined using isotopic dilution techniques. Similarly, the isotopic composition of the U was determined by measurements of the 235U/238U isotopic ratio. The quantity of 237Np in the sample was determined using a set of external standards as well as measurements of the chemical yield (recovery) of the Np, which were determined by gamma-ray counting of the short-lived 239Np tracer. Direct comparison of the chemical recovery for Np in a set of spiked urine samples, as determined by gamma-ray counting and ICP-MS, were in good agreement with one another (±3%) and indicated that Np is recovered with good yield (85-90%). Uranium and Th isotopes were typically recovered from the cleanup procedure with efficiencies of 75-85%. The detection limits of 237Np, 232Th, 235U and 238U in a 50-mL using sample were approximately 8E-4dpm, 1E-7 dpm, 2E-6 dpm, 4E-7 dpm, respectively, for a one-minute data-acquisition cycle employing a conventional pneumatic nebulizer