Tunable fragmentation of organic molecules in laser ablation glow discharge time-of-flight mass spectrometry
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A DC-pulsed glow discharge (GD) has distinct temporal regimes which are characterized by “softer” or “harder” ionization of analytes introduced into the discharge. It is thus possible to obtain both molecular weight and structural fragment information from the same spectra. In order to extend the capabilities of this technique a laser ablation (LA) sampling system was coupled to a DC-pulsed GD and to a time-of-flight (TOF) mass spectrometer (MS) for characterizing organic samples such as oleic acid, reserpine, two different peptides, and a polymer. Both hard and soft ionization regimes were studied. These LAGD-TOFMS results were compared to matrix-assisted laser desorption ionization (MALDI) spectra using the same compounds (i.e., analytes, concentration, and matrix). It was found that LAGD offers tunable ionization and provides a reduced matrix dependence. However, the sensitivity achieved by the prototype LAGD-TOFMS was significantly lower when compared with commercially available MALDI-TOFMS instrumentation. Since LAGD-TOFMS is rather new, some technical details to increase its sensitivity are discussed.
KeywordsPulsed glow discharge MALDI Laser ablation Fragmentation Chemical speciation
The authors would like to thank the European Community for financial support through GLADNET, a Marie Curie-RTN within the FP 6, and TOFWERK AG for providing the TOF instrument. The authors also would like to thank Dr. R. Knochenmuss for the discussion of the results, and L. Bertschi (MS service, D-CHAB) for the MALDI measurements. We also like to thank H. Longerich and two anonymous reviewers for critical and constructive comments which helped to improve the manuscript.
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