Direct Uranium Isotopic Analysis of Swipe Surfaces by Microextraction-ICP-MS

Abstract

The ability to directly measure uranium isotope ratios on environmental swipes has been achieved through a solution-based microextraction process and represents a significant advancement toward the development of a rapid method to analyze international nuclear safeguard samples. Here, a microextraction probe is lowered and sealed onto the swipe surface, and analytes within the sampling site (∼8 mm 2 ) are dissolved and extracted into a flowing solvent of 2% nitric acid (HNO 3 ). The mobilized species are subsequently directed into an inductively coupled plasma-mass spectrometer (ICP-MS) for accurate and precise isotope ratio determination. This work highlights the novelty of the sampling mechanism, particularly with the direct coupling of the microextraction probe to the ICP-MS and measurement of uranium isotope ratios. The preliminary method detection limit for the microextraction-ICP-MS method, utilizing a quadrupole-based MS, was determined to be ∼50 pg of 238 U. Additionally, precise and accurate isotope ratio measurements were achieved on uranium reference materials for both the major ( 235 U/ 238 U) and minor ( 234 U/ 238 U and 236 U/ 238 U) ratios. While the present work is focused on directly measuring uranium isotopic systems on swipe surfaces for nuclear safeguards and verification applications, the benefits would extend across many applications in which direct solid sampling is sought for elemental and isotopic analysis.

Analysis of solid uranium particulates on cotton swipes with an automated microextraction-ICP-MS system

“…30 A different direct analysis technique, microextraction-ICP-MS, has been explored for the measurement of uranium and plutonium isotope ratios on simulated ES swipes. [33][34][35] Marcus et al analyzed U, deposited as solution residues, on swipes with a microextraction system coupled to a liquid samplingatmospheric pressure glow discharge (LS-APGD) microplasma 36 ionization source and an orbitrap mass spectrometer. 35 Regarding the microextraction-ICP-MS methodology, major and minor U isotope ratios of several certied reference materials were extracted from a cotton swipe containing deposited U solution, and preliminary detection limits were determined to be ∼50 pg for 238 U.…”

“…37 The uncertainty of the quadrupole ICP-MS isotope ratio measurements was also evaluated with larger sample sizes compared to previous work. 33,34,37…”

“…35 Regarding the microextraction-ICP-MS methodology, major and minor U isotope ratios of several certified reference materials were extracted from a cotton swipe containing deposited U solution, and preliminary detection limits were determined to be ∼50 pg for 238 U. 34 Pu isotope ratios were determined on a cotton swipe by microextraction integrated with a sector field ICP-MS, and with detection limits for Pu in the sub-pg range. 33 Microextraction was also proven to successfully determine uranium isotope ratios for solid particulates of uranyl nitrate and uranyl fluoride placed on the surface of a cotton swipe.…”

Direct, multielement determinations from cotton swipes via plate express microextraction coupled to an inductively coupled plasma mass spectrometer (μEx-ICP-MS)

“…A collaboration between this laboratory and the Oak Ridge National Laboratory (ORNL) introduced a simple method of extracting solution residues and particulates from standard cotton swipes for the determination of uranium and plutonium isotope ratios. 32 The approach was based on the use of the Advion (Ithaca, NY) plate express as a means of solutionmicroextraction from a cloth substrate and transporting the eluate rst to a liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma ionization source, 32 and more recently to ICP sources, [33][34][35][36] for MS detection. The device was originally designed as a means of extracting organic species from thin layer chromatography (TLC) plates, 37,38 for their transport to electrospray ionization (ESI) sources for qualitative analysis.…”

“…Following the initial demonstration with the LS-APGD/Orbitrap coupling, more extensive reports from Manard and co-workers have described the performance of the swipe sampling methodology towards U and Pu isotopic analysis on a variety of ICP-MS instrument platforms. [33][34][35][36] The microextraction with plasma MS detection has proven to be simple and quantitative, requiring virtually zero sample preparation, with LODs, precision, and sensitivity that is quite sufficient for most U/Pu nuclear forensics applications.…”