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

The glow discharge ionization source operated in the pulsed (or modulated) power mode offers unique characteristics not available from its steady stat e counterpart. It has been well established that higher instantaneous power densities are obtainable without compromising the sample integrity when pu lsed plasmas are implemented. This operating parameter affords higher sputt er yields and lower limits of detection relative to the steady state plasma s. Of special interest are the discrete temporal regions associated with th e modulated plasma. The presence of these time regimes offers temporal sele ctivity, allowing the collection of analytical data in a region where the c ontribution from background and contaminant species is minimized. These reg ions are characterized by strikingly different ionization mechanisms. Acqui sition of data during each of these temporal regimes provides both molecula r and elemental information. In this work the potential use of the pulsed g low discharge for collecting concurrent molecular and elemental information was explored. This task was accomplished using time-of-flight mass spectro metry (TOFMS). TOFMS has a significantly high throughput and duty cycle, ma king it ideally suited for rapid acquisition of spectra. This characteristi c allows data acquisition during each of these temporal regions for each di scharge pulse power cycle, affording concurrent elemental and molecular det ection. p-Xylene was used as a test molecule for these studies.