| AVS 59th Annual International Symposium and Exhibition | |
| Applied Surface Science | Thursday Sessions |
| Session AS-ThM |
| Session: | Applications of Large Cluster Ion Beams |
| Presenter: | M. Dürr, University of Applied Sciences Esslingen, Germany |
| Authors: | B.-J. Lee, University of Applied Sciences Esslingen, Germany M. Baur, University of Applied Sciences Esslingen, Germany C.R. Gebhardt, Bruker Daltonik GmbH, Germany M. Dürr, University of Applied Sciences Esslingen, Germany |
| Correspondent: | Click to Email |
Desorption and ionization induced by neutral cluster impact is a very soft method for transferring surface-adsorbed biomolecules into the gas phase [1]. The neutral clusters with a mean size of 103 to 104 molecules are seeded in a He beam which results in a narrow velocity distribution and an energy density of 0.5 to 0.8 eV/molecule. Using SO2 clusters, the method furthermore makes use of the dipole moment of the cluster's constituents which allows both for solvation and charge transfer processes in the cluster. Thus the cluster provides not only the energy for the desorption process but also serves as a transient matrix. As a consequence, desorption and ionization of oligopeptides and proteins is observed at comparably low energies of the impacting clusters and without any fragmentation of the biomolecules.
In order to quantify the ionization probability during cluster-induced desorption and ionization, samples with well defined amount of substance, especially oligopeptides such as angiotensin II and bradykinin, were prepared by means of drop casting the respective solution on a SiO2 surface. A biased grid in front of the target was used to transfer ions of one polarity into the time-of-flight mass spectrometer; simultaneously, the correlated ion current from the target was measured. In case of oligopeptides, the positive ion signal is dominant and both positive ion mass spectra and extracted charge per pulse were measured as a function of the number of cluster pulses applied. Comparison of the total charge desorbed from the respective sample with the amount of substance applied then yields the ionization efficiency which was found to be 3 to 4 % in the case of the investigated oligopeptides. The result is discussed with respect to the desorption and ionization mechanism during cluster-surface impact, taking into account the influence of functional groups and preparation conditions.We furthermore show that desorption and ionization induced by neutral cluster impact can be successfully combined with ion trap mass spectrometry for applications in bioanalytics. Especially when the cluster beam is produced by a pulsed nozzle with pulse duration in the sub-millisecond regime, all ions generated during one pulse can be collected in the ion trap. In combination with the high ionization efficiency of the process, femtomol sensitivity was achieved in the case of various oligopeptides; multiple sample arrays and low sampling time then allows for batch-type analysis of biosamples.
[1] C. R. Gebhardt, A. Tomsic, H. Schröder, M. Dürr, and K.L. Kompa, Angew. Chem. Int. Ed. 48, 4162 (2009).