Rapid paper spray mass spectrometry characterization of uranium and exemplar molecular species

The ability to detect and quantify the presence of specific inorganic elements and complexes is essential for environmental monitoring and nuclear safeguards applications. In this work, paper spray ionization mass spectrometry was used for the rapid chemical and isotopic characterization of trace inorganic species collected on cotton swipe substrates. The direct analysis of cotton swipes using this ambient ionization technique led to fast sample analysis that retained original chemical information of the source material with minimal sample preparation.

Mass spectra were collected with an atmospheric pressure ionization, high-resolution mass spectrometer for solutions containing uranyl acetate, uranyl chloride, uranyl nitrate, and uranyl tri-n-butylphosphate complexes. Gadolinium nitrate was used as an internal standard for the quantitative analysis of uranium. To demonstrate the ability to characterize inorganic contaminants in the presence of uranium, a multi-element inorganic standard containing U, Bi, Pb, Cd, Fe, and Zn was deposited onto cotton substrates and directly analyzed without purification.

All elements doped on the cotton substrate were detected with strong signal-to-noise ratios (ca 1000 for UO₂ ⁺ on multi-element doped swipes) and high integrated intensities (>10⁵ counts) from collection periods of approximately 1 min. Limits of detection were determined to be approximately 94 ng for UO₂ ⁺ and uranyl acetate through the measurement of ppb level solutions.

The rapid analysis of uranium and other inorganic-containing samples while still retaining original chemical information (e.g. uranyl complexation) was demonstrated. Qualitative detection and speciation were achieved in less than 1 min of analysis. For uranium isotopic quantitation, longer accumulations (>15 min) can be sustained to improve the accuracy of minor ²³⁵ U isotopic abundance measurements to approximately 1% error.