P. Håkansson

Low-mass ions observed in plasma desorption mass spectrometry of high explosives

The low-mass ions observed in both positive and negative plasma desorption mass spectrometry (PDMS) of the high explosives HMX, RDX, CL-20, NC, PETN and TNT are reported. Possible identities of the most abundant ions are suggested and their presence or absence in the different spectra is related to the properties of the explosives as matrices in PDMS. The detection of abundant NO+ and NO2- ions for HMX, RDX and CL-20, which are efficient matrices, indicates that explosive decomposition takes place in PDMS of these three substances and that a contribution from the corresponding chemical energy release is possible. The observation of abundant C2H4N+ and CH2N+ ions, which have high protonation properties, might also explain the higher protein charge states observed with these matrices. Also, the observation of NO2-, possibly formed by electron scavenging which increases the survival probability of positively charged protein molecular ions, completes the pattern. TNT does not give any of these ions and it is thereby possible to explain why it does not work as a PDMS matrix. For NC and PETN, decomposition does not seem to be as pronounced as for HMX, RDX and CL-20, and also no particularly abundant ions with high protonation properties are observed. The fact that NC works well as a matrix might be related to other properties of this compound, such as its high adsorption ability.

Electron capture dissociation of substance P using a commercially available Fourier transform ion cyclotron resonance mass spectrometer

Electron capture dissociation of the peptide Substance P is reported for the first time, with an unmodified, commercially available Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. The fragmentation pattern is compared with that obtained with collisionally induced dissociation of the ions in the electrospray ion source, and note that electron capture dissociation gives a more easily interpreted spectrum, showing mainly C-fragments. With the exception of the proline residues, which require cleavage of two chemical bonds, we observe all C-fragmental we find the bias voltage of the electron gun not to be very critical.

Acceleration of Cn+60 molecules to high energy

Abstract For the first time fullerene ions have been accelerated to high energy (4–36 MeV). Negative ions of C − 60 were produced in an ion source with a Cs gun and injected into a tandem accelerator. The change of charge from negative to positive was achieved by collisions with N 2 molecules in a gas cell at the high voltage terminal before the second acceleration step. To identify the accelerated molecular ions, the injected beam was pulsed, and time-of-flight measurements combined with energy measurements allowed mass and charge assignments.

Automatic analysis of hydrogen/deuterium exchange mass spectra of peptides and proteins using calculations of isotopic distributions.

High mass-resolving power has been shown to be useful for studying the conformational dynamics of proteins by hydrogen/deuterium (H/D) exchange. A computer algorithm was developed that automatically identifies peptides and their extent of deuterium incorporation from H/D exchange mass spectra of enzymatic digests or fragment ions produced by collisionally induced dissociation (CID) or electron capture dissociation (ECD). The computer algorithm compares measured and calculated isotopic distributions and uses a fast calculation of isotopic distributions using the fast Fourier transform (FFT). The algorithm facilitates rapid and automated analysis of H/D exchange mass spectra suitable for high-throughput approaches to the study of peptide and protein structures. The algorithm also makes the identification independent on comparisons with undeuterated control samples. The applicability of the algorithm was demonstrated on simulated isotopic distributions as well as on experimental data, such as Fourier transform ion cyclotron resonance (FTICR) mass spectra of myoglobin peptic digests, and CID and ECD spectra of substance P.

Radiation damage features on mica and L-valine probed by scanning force microscopy

The radiation damage tracks on the surface of muscovite mica due to single 78.2 MeV 127I ions from the Uppsala EN tandem accelerator have been studied using tapping mode scanning force microscopy (TM-SFM). Conically-shaped hillocks having nearly circular bases were observed on a sample irradiated at normal incidence. Samples irradiated at grazing angles of incidence displayed wider and taller hillocks, and each hillock was accompanied by a raised tail over the bulk ion track. First SFM results are also presented from a study of radiation damage features on mica and single crystals of L-valine induced by single 23 MeV C60 ions from the Orsay tandem accelerator. Brief comments are made on the scaling laws that could link results obtained with atomic and cluster ions.

A 9.4 T Fourier transform ion cyclotron resonance mass spectrometer: description and performance

9.4 Tesla Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers (Bruker BioAPEX-94e) have been installed at the Division of Ion Physics, Uppsala University, and at the Department of Chemistry, University of Warwick. The BioAPEX-94e FT-ICR instrument is built around a high-field, superconducting magnet and a platform with easily interchangeable ion sources [matrix-assisted laser desorption/ionisation (MALDI), secondary ion mass spectrometry (SIMS), electrospray ionisation (ESI) and electron impact/chemical ionisation (EI/CI)]. In this paper a technical description of the instrument is given. Outstanding performance characteristics are demonstrated, notably clear resolution of C59N+ and C5813C2+ (mass difference 3.65 mDa) and mass measurement accuracy at the low ppm level. A wide range of applications in Warwick and Uppsala is described, demonstrating the versatility and high performance of the instrument.

An MeV-ion implanter for large area applications

Abstract A facility for MeV ion irradiation of large areas (10 × 10 cm2) is described. Irradiation with a variety of ion beams at fluences ranging from 108 to 1015 ions/cm2 can be conducted with less than 5% variation in dose. The system is presently used for charge-carrier lifetime control in semiconductors and for studies of thin film adhesion enhancement.

Total molecular yields for fast heavy ion induced desorption of biomolecules

Abstract The total desorption yield for intact molecules of the amino acid leucine (131 amu) induced by 90MeV 127I14+ ions has been studied. A collector method was used where the collector samples were analysed using both an amino acid analyzer (via optical absorption) for absolute measurements and Plasma Desorption Mass Spectroscopy for relative measurements of the total number of unfragmented molecules. Results indicate high yields of intact molecules of the order of one thousand which corresponds to a removal of about 1 × 105 A3 of sample material per incident ion. It has been shown that fast heavy ion induced desorption of leucine is essentially a “neutral ejection” process with the generally studied ionized portion constituting a very small fraction (≈1:104).

Molecular size effects in fast heavy ion induced desorption of biomolecules

Abstract Fast ion induced desorption yields of positive secondary ions of different biomolecules have been studied with a time-of-flight technique. The yields were studied as a function of energy deposition of the primary ion. The samples used were an amino acid, two protected oligonucleotides and a small protein (bovine insulin). Different primary ions with constant velocity were used throughout the experiment. In this way the energy density or electronic stopping power was changed by using different primary ions. It was found that for low energy densities the yields increase with different powers of the energy density for the different systems. For high energy densities the yields are proportional to the energy density for all systems studied. The results indicate that for large molecules multiple bond breaking is needed for desorption to occur. For the amino acid sample (valine) an extensive clustering effect was also found. Cluster ions containing as many as 20 valine molecules were observed. This wor...

Formation of fullerenes in MeV ion track plasmas

Abstract MeV primary 127 I 14+ ions from the Uppsala EN-tandem accelerator were used to bombard a polymer — poly (vinylidene difluoride). Positive ions of even numbered carbon clusters (C + n , n =40−120) are ejected as a result of the interaction of fast MeV ions with the organic solid. The distribution of cluster sizes suggests that stable, closed carbon-cage structures — fullerenes — are formed. Initial radial velocity distributions of the desorbed carbon species are consistent with preferential ejection backward into the direction of the incoming MeV ions. Correlation between the directions of incoming particles and ejected clusters suggests that the latter (including C + 50 and C + 60 ) originate in the infratrack plasma produced by the fast primary ions interaction with the sample. A main conclusion resulting from this study is that carbon cluster ions form as a result of a single primary ion impact and that they are ejected from an axially expanding infratrack plasma region.