Advances in plasma source mass spectrometry with a time-of-flight mass analyzer.

摘要

A staple of plasma source mass spectrometry (PSMS) for over 15 years, inductively coupled plasma mass spectrometry (ICPMS) is widely recognized in elemental analysis for its exceptional capabilities: multielemental determinations with low detection limits (∼10--100 fg/mL), a linear dynamic range reaching 108, and an applicability to a wide range of sample types and sampling conditions. The direct analysis of solid samples via glow discharge (GD) sources further extends the utility of PSMS. The desire to rapidly perform sensitive determinations while simultaneously collecting an ever-greater amount of chemical information motivated the evolution from simple bulk determinations of elemental composition to sophisticated methods that offer micro-, spatially resolved, and time-resolved analyses. In this suite of methodologies, the sample concentration often changes during the analysis, and these transient methods place new demands on instrumentation. The continued success of PSMS depends on its ability to adapt to these challenges, and alternative mass analyzers, such as time-of-flight mass spectrometry (TOFMS), have been explored as a means to meet such demands.; In TOFMS, all ions are extracted for mass analysis simultaneously, and when it is used for elemental analysis, over 20,000 complete mass spectra can be generated each second. These characteristics have resulted in the emergence of PS-TOFMS as an analytical tool particularly well suited for transient analyses. Moreover, these attributes can be exploited to overcome existing problems in PSMS, the premise for the work presented in this thesis. The effect of the plasma operating frequency on the analytical performance of a commercial ICP-TOFMS system is investigated. A method for characterization of matrix interferences that routinely impair analysis in ICPMS is detailed along with a method for diagnosing and alleviating them. Additionally, a standardless semiquantitative analysis technique is described that overcomes the lack of appropriate standards for GDMS. An improved directly digital flow controller that permits gas-flow modulation up to 10 Hz is detailed. Lastly, a method for improving overall sensitivity while also reducing analysis time by modulation of plasma parameters is presented.