Consideration of a millisecond pulsed glow discharge time-of-flight mass spectrometer for concurrent elemental and molecular analysis

Abstract

The glow discharge ionization source operated in the pulsed (or modulated) power mode offers unique characteristics not available from its steady state counterpart. It has been well established that higher instantaneous power densities are obtainable without compromising the sample integrity when pulsed plasmas are implemented. This operating parameter affords higher sputter yields and lower limits of detection relative to the steady state plasmas. Of special interest are the discrete temporal regions associated with the modulated plasma. The presence of these time regimes offers temporal selectivity, allowing the collection of analytical data in a region where the contribution from background and contaminant species is minimized. These regions are characterized by strikingly different ionization mechanisms. Acquisition of data during each of these temporal regimes provides both molecular and elemental information. In this work the potential use of the pulsed glow discharge for collecting concurrent molecular and elemental information was explored. This task was accomplished using time-of-flight mass spectrometry (TOFMS). TOFMS has a significantly high throughput and duty cycle, making it ideally suited for rapid acquisition of spectra. This characteristic allows data acquisition during each of these temporal regions for each discharge pulse power cycle, affording concurrent elemental and molecular detection. p-Xylene was used as a test molecule for these studies.