Alternative Ionization Methods for Particle Mass Spectrometry
The objective of this project is to enhance the capabilities of a real-time airborne particle mass spectrometer by implementing matrix-independent methods for sample ionization. The enhancements should result in improved sensitivity for trace substances and, more importantly, permit quantitative determination of the presence of target species in microparticle samples on an individual particle basis. We have used two different approaches to eliminate matrix effects on quantitative accuracy. Both rely on delayed ionization of ablated/desorbed neutral species so that ionization of target substances occurs after most of the expansion collisions have taken place. Resonance ionization by a tunable pulsed laser permits selective ionization of target species, with the laser tuned to a resonance transition from the ground state to an excited state of the target. Additional photons of the same (when possible) or different energy make up the energy required for ionization. The other approach is to perform the laser ablation step within a discharge so that desorbed neutrals are ionized by reactions with the plasma. Electron capture generates negative ions of substances with high electron affinity while electron impact ionization, associative ionization, and Penning ionization from excited metastable species produce positive ions in the discharge. Both atmospheric pressure Corona discharge ionization and glow discharge ionization at reduced pressure are being explored. Discharge ionization is relatively nonselective so that target specificity must be obtained through the mass spectral or MS/MS results.
- Research Organization:
- Oak Ridge National Lab., Oak Ridge, TN (US)
- Sponsoring Organization:
- USDOE Office of Science (SC) (US)
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 838675
- Report Number(s):
- EMSP-82792-2004; R&D Project: EMSP 82792; TRN: US0501487
- Resource Relation:
- Other Information: PBD: 1 Jun 2004
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
54 ENVIRONMENTAL SCIENCES
ANIONS
ATMOSPHERIC PRESSURE
CATIONS
CORONA DISCHARGES
ELECTRON CAPTURE
ELECTRONS
EXCITED STATES
GLOW DISCHARGES
GROUND STATES
IONIZATION
MASS SPECTROMETERS
MASS SPECTROSCOPY
MESONS
PARTICULATES
PHOTONS
RESONANCE