Isotope analyses are often leveraged in archeology, ecology, and forensic science applications, as well as in national security and nuclear energy applications. Although, conventional isotope-ratio mass spectrometry (IRMS) – is typically lab-based, the life-threatening nature of radio-nuclear activity from nuclear fuel feedstock, spent fuel, and post detonation debris calls for a field deployable analytical approach. Differential mobility spectrometry (DMS) has been a promising analytical technique for field sampling, filtration, and analysis of target analytes from their native state on the order of milliseconds. In earlier studies, we have demonstrated the DMS-MS hybrid for metal speciation and differentiation from chemical interferences. Herein, uranyl ion and other fission products shall be characterized. Furthermore, isotopic measurements shall be conducted on each ionic species. A DMS-cell comprised of two electrodes (15 mm × 4 mm) separated by 0.5 mm gap was interfaced with a commercial ion trap MS (Thermo LTQ XL). Commercial electronics from Sionex supplied the RF and DC potentials to the electrodes representing the dispersion voltage (DV) and compensation voltage (CV) parameters, respectively. The interface was designed to accommodate external pumping to control the transport gas flow through the DMS drift region. Uranyl nitrate salt, d and f block metals (analogous to fission fragments) were prepared in solution. Two ionization methods were employed: 1) electrospray ionization at 1 µL/min sample flow rates and 2) Flowing Atmospheric Pressure Afterglow (FAPA) desorption/ionization across of dried sample applied to a stainless steel mesh. For a nanosprayed solution mixture containing Uranium and Strontium, a dispersion plot was obtained within ~ 5 minutes. At a fixed DV 1000 V, UO2+ and SrOH+ were filtered out at -8.6 and -11.5 V, respectively. The corresponding mass spectrums obtained have a reduced chemical interference when compare to DMS off. Furthermore, isotopy study was conducted on UO2+ ion at DMS off and on (fixed DV and CV of 1000 V and -8.6 V, respectively) for ~30-minute run time. With DMS off, 235U/238U ratio was measured as 0.349. The extremely high result was due to an unknown chemical interfering peak (m/z 267) associated with the 235UO2+ ion. While DMS is on, 235U/238U ratio was measured as 0.007. The result obtained indicates that DMS coupled to a trap-based MS is a promising on-site analytical tool for isotopy measurement.

Differential mobility spectrometry-mass spectrometry for isotope ratio analysis

2019 Spring National Meeting

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