Development of a Field-Deployable Mass Spectrometry System for Nuclear Forensics Applications Using Liquid Sampling–Atmospheric Pressure Glow Discharge as an Ion Source

Abstract

There is a need for in-field actinide measurements in support of nuclear forensic, safeguards, and environmental monitoring missions. Traditional methods of inorganic/elemental analysis, such as inductively coupled plasma mass spectrometry (ICP-MS), have high operational overheads, making these platforms ill-suited for this task. The liquid sampling–atmospheric pressure glow discharge (LS-APGD) ionization source is a proven microplasma ionization source with significantly reduced operational overhead as compared to ICP-MS; however, most studies to date have focused on coupling the LS-APGD to an ultrahigh resolution Orbitrap mass spectrometer. While the Orbitrap mass spectrometer is a benchtop instrument, it is quite complex with a large footprint and requires extremely low mass analyzer pressures. The Advion Expression^L compact mass spectrometer (CMS) is a compact, easily transported single quadrupole mass spectrometer platform that was previously coupled with the LS-APGD to measure multielement/metal solutions, albeit not actinides. To this end, this manuscript reports the optimization of the LS-APGD with the Advion Expression^L CMS mass spectrometer platform specifically for in-field actinide (uranium and thorium) measurements. This is the first report on the optimization of the dual-electrode LS-APGD on the CMS, including a modified ion sampling geometry. This also includes the first analysis of thorium using the LS-APGD, regardless of mass spectrometer coupling. After establishing that the LS-APGD and the mass spectrometer operations could be optimized independently, the LS-APGD discharge conditions were optimized with a design of experiments approach, with the mass spectrometer parameters optimized by a full factorial study. Once fully optimized, limits of detection of 0.2 ng total analyte mass were found for both uranium and thorium, below the EPA requirements for drinking water.

Graphical abstract

This is a visual representation of the abstract.