Date of Graduation
Eberly College of Arts and Sciences
Fred L. King.
Most modern analytical techniques are derived from coupled methods involving a chromatographic separation followed by mass spectrometric detection. These techniques are employed in modern laboratories in the form of gas and liquid chromatography mass spectrometric systems. Chromatography methods separate and concentrate different chemical species based on phase partitioning. Once separated, the sample is analyzed mass spectrometrically, where further information and identification of the analyte may be deduced based on its inherent mass-to-charge ratio. However, following chemical separation and previous to any mass spectrometric detection, the analyte most be ionized. To date there are numerous possible methods for ionization, however, they can be classified into hard and soft ion sources.;The common ionization method is electron ionization (EI) in which the compound is atomized or fragmented. This method readily provides both elemental and structural information, because compounds of the same class will have similar elemental compositions and fragmentation patterns. In contrast, soft ionization, such as chemical ionization (CI), yields molecular weight information because the unfragmented molecule is ionized and detected intact. It is easy to see that these two methods provide complementary information. To date, no ion source has been developed that grants both EI and CI characteristics simultaneously and independently of one another.;In these investigations the pulsed glow discharge source has demonstrated an ability to permit the separation of electron-ionized species from Penning ionized species. Penning ionization is a relatively soft ionization process, where analyte molecules are ionized by collisions with metastable argon atoms. In pulsed glow discharge plasmas these two processes are separated both temporally and spatially. The analytical advantage of the separation of these two processes can be illustrated in the discrimination of isobaric interferences using time-gated detection, an example would be the determination of 40Ca + from 40Ar+. Further exploitation of these temporal regimes can be applied to molecular analysis, where concurrent molecular and structural information can be obtained.
Lewis, Cris Lee, "Characterization and applications of pulsed millisecond glow discharge sources" (2000). Graduate Theses, Dissertations, and Problem Reports. 1234.