Explicit chemical speciation by microsecond pulsed glow discharge time-of-flight mass spectrometry: concurrent acquisition of structural, molecular and elemental information

A microsecond pulsed glow discharge (mu s-pulsed GD) was used for elemental , structural and molecular analysis. This plasma was generated repeatedly a t 100 Hz with a 1 kV electrical pulse lasting 20 mu s. Samples were continu ously introduced into the mu s-pulsed discharge and allowed to interact wit h the plasma. Depending on the extent of this interaction, which is control lable at the discretion of the user, the samples may undergo soft chemical ionization yielding molecular ions or may be completely atomized and ionize d yielding elemental information. The operator could choose the above inter action zones or anything in between, which provides structural information through an electron ionization type fragmentation pattern. Detection of pla sma produced ions was done by time-of-flight mass spectrometry (TOF-MS), wh ich is most suitable for complete mass spectrometric analysis of time-gated transient events. Using ion energetic information and the so-called 'therm ometer molecules', the magnitude of ionization energy available in the disc harge was calculated. At 60 mu s after the plasma ignition the plasma had a n equivalent ionization energy of about 17 eV. The plasma energy decreased as a function of time. At about 300 mu s the plasma reached a relatively co nstant ionization energy of 8-9 eV, which lasted for nearly 200 mu s. Tolue ne, p-xylene, ethylbenzene and tungsten hexacarbonyl are among the molecule s analyzed using time-gated mu s-pulsed GD-TOF-MS.