International Journal of Mass Spectrometry and Ion Physics最新文献

After a short survey of the historical development of organic SIMS, the main experimental results of organic secondary ion formation are summarized in the frame of a precursor model. Results of static SIMS investigations of the (M+H)⁺ -, (M−H)⁻ -, and (M−H)⁺ - emission from metal supported amino acids and of different organic compounds in a glycerol matrix are reported. The performance of a new time-of-flight instrument for SIMS is demonstrated.

High energy ion bombardment of organic compounds in the condensed phase is foundto gice rise to secondary molecular ions in the gas phase containing appreciable internal energy of excitation. This paper presents the results of time-of-flight mass spectrometric studies of the subsequent prompt and metastable decomposition of these excited ions. The implications of the findings on the fragmentation mechanisms involved in heavy particle bombardment mass spectrometry is discussed.

Some properties of the Manitoba time-of-flight secondary ion mass spectrometer are described and compared with those of other instruments. Topics discussed include properties of the primary ion beam, preparation of small electrosprayed targets, secondary ions from alkali halides (metastable decay and increase in yield after irradiation), data handling and sensitivity.

Californium-252 plasma desorption mass spectrometry is reviewed in its application to a series of natural products including fungal metabolites, toxins, and nucleosides. Its importance in identifying the molecular weight of an unknown compound early in isolation procedures is emphasized. Several new applications to synthetic peptides, a dye conjugate and cardiac glycosides are illustrated.

This opening lecture in the Texas Symposium on Particle Induced Desorption is intended to reflect on the state of the art, and to pose questions to the instrumentalists, the theoreticians and the analytical/bioorganic chemists participating in the three respective subdivisions of the symposium. Recent studies from our laboratory are discussed which investigate the information which can be deduced from the molecular ion envelope of an unknown middle mass or large molecule, evaluate the need for unit resolution above 5000 amu, and illustrate the ability of particle induced desorption to provide stable isotope analyses, absolute and relative quantitation in mixtures, as well as molecular weights and structural information.

Positive secondary ion mass spectra of neat solid O₂ and O₂ diluted with argon at 15–20K were measured as a function of the nature and energy of the primary ions (He⁺, Ar⁺, Kr⁺, 0.5–4.0 keV). With He⁺, the spectrum of solid O₂ is dominated by O₂ and O⁺ peaks, with Ar⁺ and Kr⁺, it is dominated by an intense cluster series O⁺_3n+2, n = 0,1,2….

Accurate mass measurement at a resolution of 10,000 has been performed with very small ion currents generated by fast atom bombardment ionization. With the use of a peak matching unit to switch accelerating voltage and a multi-channel analyzer to acquire the data, determination of exact mass can be routinely made with less than 5 ppm error on ion currents of insufficient intensity for accurate peak matching in the conventional mode. Glycerol cluster ions generated during the FAB experiment are suitable mass references. Calibration of the peak matching unit voltage offset allows the use of a single reference mass for exact mass calculation.