Spark-Source Mass Spectrometry (SSMS) for Matrix-Free Cation and Anion Elemental Sample Analysis

Current state-of-art inductively-coupled plasma (ICP) elemental mass spectrometric analyzers for nuclear forensic analysis typically fall into two categories: (i) quadrupole based ICP mass analyzers, and; (ii) magnetic sector based ICP mass analyzers. While both systems have many benefits and drawbacks, the primary differences are price, full mass range vs. specific ion collection capabilities, dynamic range, and the general limitation that only positive ions can be analyzed. While ICP provides an extremely powerful analytical tool, this technique is sometimes limited by: (i) matrix effects, (ii) time-consuming sample preparation, and (iii) that large sample sizes are required to interrogate trace-level constituents. While not a new technique, we present here a modernized design for implementation of arc-based ionization mass spectrometry with the goal of significantly reducing sample preparation time and achieving simultaneous full mass range analysis with minimal matrix effects. In addition, using tandem time-of-flight mass spectrometry (TOF) techniques allows for the ability to analyze major and trace-level elemental impurities, including halogens, with significantly improved accuracy and precision over historical spark-source mass spectrometers. Due to the high energies associated with arc-based ionization processes (typically 250-500 eV initial ion energy), an orthogonal TOF/ReTOF mass analyzer configuration was constructed. Here an initial ion packet (from arc ionization events) is separated in the first TOF stage, then accelerated into a reflectron (energy filtering) TOF stage for mass analysis at a resolution >3000. As with historical SSMS, this mass spectrometer is capable of complete elemental impurity analysis of small samples, while still maintaining ppm to sub-ppm detection limits for many elemental constituents. Multiple detector systems are being tested (chevron and z-stack MCP, discrete dynode, etc.) under different configurations to determine the optimal instrumental dynamic range and sensitivity. The accompanying oral presentation will discuss the TOF ion optical design, instrument operation, as well as the results from initial studies designed to determine the detection limits, matrix effects and interferences to accurate measurement.