Precise ruthenium fission product isotopic analysis using dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS)

Abstract

surface environments and is a key contributor to long-term risk. However, as a mono-isotopic fission product, 99 Tc is limited in its use as a signature to differentiate between different waste disposal pathways that could have contributed to sub-surface contamination at these facilities. Ruthenium fission-product isotopes are attractive analogues for the characterization of 99 Tc sources because of their direct similarity to technetium with regard to subsurface mobility, their large fission yields, and low natural background concentrations. We developed an inductively coupled plasma mass spectrometry (ICP-MS) method capable of measuring ruthenium isotopes in groundwater samples and water extracts of vadose zone sediments. Samples were analyzed directly on a PerkinElmer ELAN DRC II ICP-MS after a single pass through a 1-ml bed volume of Dowex AG 50W-X8 100-200 mesh hydronium-based cation exchange resin. Precise ruthenium isotopic ratio measurements were achieved using a low-flow Meinhard-type nebulizer and long sample acquisition times (150 000 ms). Relative standard deviations of triplicate replicates were maintained at less than 0.5% when the total ruthenium solution concentration was 0.1 ng ml À1 or higher. Further work was performed to minimize the impact caused by mass interferences using the dynamic reaction cell (DRC) with O 2 as the reaction gas. Aqueous concentrations of 96 Mo and 96 Zr, two potential interferents to the analysis of total ruthenium concentration, were reduced by more than 99.7% in the reaction cell prior to injection of the sample into the mass analyzer quadrupole. The DRC was used in combination with mass correction to quantitatively analyze samples containing up to two orders of magnitude more zirconium and molybdenum than ruthenium. The analytical approach documented herein provides an efficient and cost-effective way to precisely measure ruthenium isotopes and quantitate total ruthenium (natural versus fission-product) in aqueous matrixes.

Geochemical Processes Data Package for the Vadose Zone in the Single-Shell Tank Waste Management Areas at the Hanford Site

“…These results were considered preliminary because the focus of Brown et al (2006s) was on method development. However, the ruthenium isotope analyses suggest a relationship between the vadose zone contamination near tank T-106 and the shallow groundwater contamination (Brown et al 2006a). …”

“…This process, however, appears to be suppressed when tank waste contacts Hanford vadose zone sediment. It is typically observed that, in the absence of reduction, the monovalent oxyanions 101,102,104 (Brown et al 2006a) have been used to trace tank waste migration through the vadose zone and serve as indicators of tank waste contamination in groundwater (Dresel et al 2002).…”

“…No fission component was seen in the molybdenum analyses, which suggests that the fission molybdenum was separated from the waste stream because a shift in ratios from the natural abundance would likely have been seen if fission molybdenum were present in proportion to the fission ruthenium. Brown et al (2006a) reported further developments on the methods to determine ruthenium isotopic ratios in groundwater and vadose zone leach samples. Samples from the WMA T vadose zone near tank T-106 and downgradient groundwater were analyzed for ruthenium isotopic ratios.…”

Geochemical Characterization Data Package for the Vadose Zone in the Single-Shell Tank Waste Management Areas at the Hanford Site

“…However, innovative approaches, such as analyses of certain stable and radioactive isotope concentrations and signatures are now being used. These studies employ advanced analytical techniques and instrumentation to enable better "fingerprinting" of contaminant plumes, making identification of contaminant source terms plausible (Brown et al 2006b, Cantrell et al 2007). While the use of "fingerprinting" at the Hanford Site is still relatively new, it has the potential to provide significant support in defining the current and future risks associated with contamination currently residing in the vadose zone.…”

Oxygenation Mechanism of Ions in Dynamic Reaction Cell ICP-MS

“…2 Interferences caused by coexisting compounds in samples can be avoided by sample pretreatment in which the interfering compounds are removed by, for example, coprecipitation or ion-exchange. [3][4][5] Uses of a desolvation apparatus for sample introduction, of a low-temperature plasma, and a high-resolution mass spectrometer are effective ways of reducing and removing interferences. [6][7][8][9][10][11] In recent years, methods employing collision/reaction gas cells using He, H2, NH3, CH4, or O2 have been introduced into ICP-MS to remove the interferences of coexisting ions.…”